7 supramolecular catalysis as a tool for green...

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7Supramolecular Catalysis as a Tool for Green ChemistryCourtney J. Hastings

7.1Introduction

Catalysis is central to advancing green chemistry in the area of synthetic chemis-try [1,2]. Beyond replacing stoichiometric reagents, catalysts have the potentialto streamline multistep synthesis by enabling new bond-forming processes toshorten synthetic sequences and achieve better step economy [3,4]. Supra-molecular catalysis and the application of supramolecular concepts to catalyticreactions is emerging as a valuable tool for improving catalytic reactions for syn-thetic chemistry. Supramolecular catalysis can enable aqueous reaction condi-tions, improve reactions selectivity, improve catalyst lifetime, and enable tandemreactions, all of which can have positive impacts on the cost, waste, and energyassociated with a reaction.The field of supramolecular chemistry concerns the design of molecular enti-

ties that are defined by reversible, noncovalent interactions. While each supra-molecular interaction is quite weak individually, the effect of many suchinteractions working in concert can produce strongly associated and structurallywell-defined molecular species [5–7]. Such additive effects are responsible forthe spectacular structural complexity found in biomacromolecules such as pro-teins. Efforts to characterize these interactions have provided chemists with a“toolbox” of reliable methods to program the association between two or moremolecules to form a single complexed species. Thus, supramolecular chemistryrepresents a complementary approach toward molecular construction, and onethat offers certain advantages over covalent chemistry [5–8].Like supramolecular interactions, host–guest binding relies on manifold non-

covalent interactions, with the added requirement that the host possess an inte-rior cavity that is complementary in size and shape to the guest molecule [9–11].Quite frequently, the “inner phase” of a synthetic host presents a dramaticallydifferent chemical environment to a bound guest than what it would experiencein the surrounding bulk solvent. In fact, the environment within a synthetic hostis frequently unlike anything that a molecule would experience in any solvent,

Handbook of Green Chemistry Volume 12: Tools for Green Chemistry, First Edition. Edited by Evan S. Beachand Soumen Kundu. 2017 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2017 by Wiley-VCH Verlag GmbH & Co. KGaA.

Handbook of Green Chemistry, Green Products, Tools for Green Chemistry, edited by Evan S. Beach, and Soumen Kundu, John Wiley & Sons, Incorporated, 2017. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/dal/detail.action?docID=4883029.Created from dal on 2017-09-29 07:02:31.

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140 7 Supramolecular Catalysis as a Tool for Green Chemistry

particularly with respect to confinement effects. Many hosts themselves are con-structed through supramolecular interactions, self-assembling from relativelysimple subunits into highly complex and symmetric structures [12–16]. Thedesign of synthetic self-assembled host molecules requires control over thegeometry of the individual components and how the components interact witheach other. This control can be achieved by choosing the subunits to interactwith each other through known and predictable noncovalent interactions.Supramolecular catalysis relies upon noncovalent interactions to provide the

primary associative interaction between catalyst and substrate, a factor that isresponsible for the spectacular selectivity and reactivity of enzymes. Supra-molecular interactions can be involved in catalysis in a number of ways. Supra-molecular encapsulation of one or more substrate molecules within a host(which itself is often self-assembled through supramolecular chemistry) can pro-mote or modulate reactivity. Supramolecular binding can enforce substrate–cat-alyst interactions through molecular recognition processes that functionindependent of the reactive functional groups. Finally, it is possible to install cat-alytic moieties within the cavity of a molecular host, which can then bind sub-strate molecules.Since the field of supramolecular catalysis and related research areas have

been the subject of many excellent reviews, the aim of this chapter is not to pro-vide a comprehensive review of supramolecular catalysis [17–39]. Rather, thegoal is to summarize the types of reaction improvements that can be made, andto provide representative examples where supramolecular catalysis was used atool for obtaining a favorable reaction outcome. Special emphasis is placed onexamples that involve widely used and synthetically useful transformations, suchas cross-coupling, hydroformylation, and C��H functionalization reactions.Finally, conceptually related work on encapsulation-mediated reaction controlusing metal–organic frameworks [40–44], the inner phase of polymers [45–48],and dendrimers [49–51], and other such species are beyond the scope of thischapter, and will be omitted.

7.2Control of Selectivity through Supramolecular Interactions

Supramolecular binding and encapsulation can exert large effects on reactionselectivity, influencing which products are formed (regioselectivity, stereoselec-tivity) and which substrates are allowed to react (substrate gating). This aspectof supramolecular catalysis parallels the high levels of selectivity achieved byenzymes, which are also due in large part due to the cumulative influence ofmany noncovalent interactions between enzyme and substrate. Imposition ofselectivity on synthetic reactions is an important goal, since separation of prod-ucts typically requires energy- or solvent-intensive purification steps. Supra-molecular control of selectivity is particularly attractive in reactions where manysites in a substrate molecule are equally reactive (e.g., C–H functionalization) or


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7.2.1

1417.2 Control of Selectivity through Supramolecular Interactions

where selectivity is difficult to achieve using traditional catalyst engineeringapproaches (e.g., photochemistry and hydroformylation). Thus, representativereactions in which supramolecular interactions improve selectivity to syntheti-cally useful levels will be the focus of this section.

Catalysis with Supramolecular Directing Groups

Reactions in which attractive substrate–reagent (or substrate–catalyst) interac-tions exist often proceed with greater selectivity or altered selectivity comparedto cases where a directing group is absent, and as such substrate-directedreactions are valuable in synthesis (Scheme 7.1) [52,53]. Typical directing groupsinfluence selectivity by binding directly to the group that is reacting with thesubstrate. In the case of transition metal catalysis, this means that the metal cen-ter is both the reactive center and the site of molecular recognition. This strategylimits the possible substrate directing groups to those that will bind to, but notinhibit the catalytic metal. A more flexible strategy is for the molecularrecognition element to be separate from the reactive center (Scheme 7.1). Inaddition to expanding the toolbox of noncovalent interactions that may be usedfor molecular recognition, this approach also enables remote functionaliza-tion [54–57], while traditional directing groups tend to favor activation of proxi-mal positions.

Scheme 7.1

This approach was pioneered by Breslow and coworkers, who developed acyclodextrin-modified Mn–porphyrin catalyst for aliphatic C��H hydroxylation.This catalyst selectively hydroxylates an unactivated position of a steroid deriva-tive (Scheme 7.2) [58]. The steroid substrate androstanediol was derivatized with


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Scheme 7.2

two ester groups bearing both water-solublizing moieties and a tert-butylphenylfor binding to the cyclodextrin. When this substrate is subjected to the catalystin the presence of iodosobenzene as the terminal oxidant in water, the steroid isregio- and stereospecifically hydroxylated. It is noteworthy that the methyleneposition where hydroxylation occurs is not the most intrinsically reactive site onthe substrate, and that supramolecular binding is responsible for the observedselectivity.Crabtree and coworkers reported a dimanganese terpyridine catalyst bearing

two molecular recognition sites for binding carboxylic acid substrates. The ter-pyridine ligands are functionalized with a phenylene group and then the Kemptriacid, which provides a U-turn geometrical element. This orients a carboxylicacid directing group that is capable of binding carboxylic acid-containing sub-strates such as ibuprofen (Scheme 7.3). The binding mode positions a singleC��H bond near the active metal center, and the substrate is regio- and stereo-selectively hydroxylated. Lower selectivity is observed when the reaction is per-formed using a dimanganese terpyridine catalyst lacking the molecularrecognition element [59].Bach and coworkers recently reported the design of a ruthenium–porphy-

rin catalyst bearing a chiral molecular recognition element. A chiral lactammoiety is linked to the porphyrin through a rigid alkyne linker and is respon-sible for binding lactam substrates (Scheme 7.4). The catalyst is capable of


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Scheme 7.3

Scheme 7.4

enantioselective C��H oxidation of prochiral spirocyclic lactam substrateswith high enantioselectivity, but modest yields [60].Recently an iridium–bypyridine complex with an attached urea group was dis-

closed by Kanai and coworkers for the catalytic C–H borylation of arenes. Thependant urea moiety complexes the carbonyl group of substrate benzamides, andthe rigid ligand framework positions the iridium center closest to the C��H bondmeta to the amide substituent (Scheme 7.5). As a result, the borylation reactionis meta-selective, while analogous complexes lacking the substrate-bindinggroup give a mixture of isomers [61].


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Scheme 7.5

Photochemical reactions are extremely valuable synthetic transformations, butcontrolling the selectivity of such reactions can be challenging. This is due to theextremely short lifetimes and high intrinsic reactivity of excited-state reactionintermediates, which provide little opportunity for directing the reaction out-come. Chiral, supramolecular triplet sensitizers have been developed by Bachand coworkers to perform enantioselective photochemical reactions. The catalystdesign links a triplet sensitizer) to a chiral lactam-binding group derived fromthe Kemp triacid, and it both ensures close contact between the sensitizinggroup and the substrate while controlling the stereochemical outcome of thereaction (Scheme 7.6). This family of catalysts enables the synthesis of enantioen-riched products via photochemical cyclization and [2+ 2] cycloaddition [62–65].

Scheme 7.6


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7.2.2


Scaffolding Ligands

As an alternative to catalyst directing groups that operate through noncovalentbonds, it is also possible to use reversible covalent bonding to colocate substrateand a metal catalyst. Scaffolding ligands, which contain both a catalyst bindingunit and a site for reversible covalent substrate binding, are used for this pur-pose [66,67]. The reversibility of the substrate binding allows the scaffolding lig-and to be used in catalytic quantities. The initial application of this approach tothe rhodium-catalyzed hydroformylation reaction was independently reported bythe groups of Breit and Tan [68,69]. The scaffolding ligands employed in thissystem contain a phosphine group for metal binding and a site for reversible,covalent bonding of substrate (Scheme 7.7).

Scheme 7.7

The reversibly bound directing group is able to effectively impose regiocontrolover the hydroformylation of homoallyllic alcohols, which is followed by oxida-tion to provide lactone products. In the absence of the scaffolding ligand, a mix-ture of products favoring the linear aldehyde, which cyclizes to form a six-membered lactone after oxidation (Scheme 7.8). The scaffolding ligand is able tooverride the intrinsic selectivity of the reaction, selectively producing thebranched product (which forms a five-membered lactone after oxidation). Thisapproach could also be applied to hydroformylation of alkene substrates bearingsulfonamide and aniline directing groups [70,71].


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7 Supramolecular Catalysis as a Tool for Green Chemistry146

Scheme 7.8

7.2.3Selectivity through Confinement and Binding Effects

The chemical environment and confined space inside of self-assembled hostscan impart selectivity to reactions mediated by supramolecular catalysts. Whencatalysis occurs within a confined space, it is possible to impart product selectiv-ity that is difficult to achieve with conventional catalysts. A second type of selec-tivity is the control over which substrates are allowed to react by limiting the sizeand shape of molecules that penetrate the host interior. Both of these types ofselectivity are also hallmarks of enzymatic catalysis.Seminal work published by the van Leeuwen and Reek groups has explored

the effect of supramolecular encapsulation on the selectivity of rhodiumhydroformylation catalysts, an important reaction in which selectivity is diffi-cult to control [72]. A monodentate tripyridylphosphine ligand is capable ofbinding a zinc porphyrin panel through each pyridine, creating a well-definedligand-templated assembly that encapsulates a phosphine-bound rhodiumcenter (Scheme 7.9). Compared to the rhodium complex without the associ-ated porphrins, the ligand-templated catalyst is more active and more selec-tive for the branched isomer. The increased selectivity produced by theencapsulated catalyst is due to the steric restrictions imposed by the assemblyinterior. A related ligand-templated assembly was created from the tris(zinc(II) porphyrin)phosphite ligand, which self-assembles in the presence of threebridging diamines to form a sandwich structure with a rhodium center in theinterior cavity. This supramolecular catalyst is an active hydroformylation cat-alyst and is highly selective for the linear hydroformylation product [73].Rebek and coworkers have designed a family of open-ended resorcinarene-

derived hosts in which a diversity of functional groups are positioned over thehost rim, protruding into the cavity. The host is functionalized with a carboxylicacid group, which is attached to the host rim and dangles into the bindingpocket (Scheme 7.10). The intramolecular epoxide ring opening of a 1,5-epox-yalcohol is catalyzed by the host to form a hydroxymethyltetrahydrofuran prod-uct [74]. The host-catalyzed reaction is substantially accelerated when comparedto the reaction catalyzed by a carboxylic acid that is electronically similar butlacks any substrate-recognizing cavity. This difference underscores the enhancedreactivity that results from enforcing the close proximity of substrate and a


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Scheme 7.9

Scheme 7.10

catalytic functional group. Additionally, the 26-catalyzed reaction produces amixture of regioisomers, the result of intramolecular nucleophillic attack at bothepoxide positions, while the host-catalyzed reaction yields a single regioisomer.An important self-assembling catalyst system for epoxide formation was pub-

lished by the Hupp and Nguyen groups. The supramolecular box self-assemblesfrom rigid porphyrin-based components and forms a large, cavity-containingstructure bearing interior manganese porphyrins [75,76]. While alkenes such asstillbene can be oxidized to the corresponding epoxide by the encapsulated cata-lyst, larger derivatives do not interact with the catalyst as easily and are undergoepoxidation less efficiently (Scheme 7.11). The ability to discriminate between


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Scheme 7.11


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substrates on the basis of size alone is due to the steric constraints imposed byencapsulation.A recent from deBruin and coworkers report detailed the cyclopropanation

behavior of a cobalt–porphyrin catalyst encapsulated within a M8L6 cubicassembly [77]. The constricted cage pores of the host modulate how easily sub-strates reach the encapsulated catalyst, with smaller substrates having easieraccess. In a competition experiment, 8:2 selectivity for the smaller substrate wasexhibited (Scheme 7.12). In contrast, no selectivity is observed when the sameexperiment is conducted with the unencapsulated catalyst.

Scheme 7.12

A micellar system disclosed by Scarso and coworkers exhibits high levels ofsubstrate selectivity in the palladium-catalyzed hydrogenation of α,β-unsaturatedaldehydes [78]. In this example, the catalytic species is a surfactant-encapsulatedPd nanoparticle. Lipophilic substrates bearing long alkyl chains react faster thanC4 and C5 substrates by a factor of 300 (Scheme 7.13). The opposite trend inreaction rates is observed when the reaction is conducted in organic solvent.This is due to their increased ability to associate with the micellar phase due tothe hydrophobic effect, allowing easier access to the catalytic nanoparticle sur-face. Similar effects are seen in the Diels–Alder and Heck reactions, catalyzed bymicelle-encapsulated Cr(III)–salen and Pd(II) catalysts, respectively [79,80].Interestingly, larger substrates react faster in these systems, in contrast to theselectivity typically seen in other supramolecular systems.


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Scheme 7.13

7.3Reactions in Water

Solvents account for a large fraction of waste generated in chemicals reactions,and switching to environmentally innocuous solvents is one of the twelve princi-ples of green chemistry [1,2,81,82]. Water is perhaps the most obvious greensolvent because it is nontoxic, nonflammable, inexpensive, and requires no syn-thesis. Despite these advantages, water is seldom used as a solvent for organicreactions because many substrates and reagents are either insoluble in orincompatible with water [83]. A related issue is that water can react with somereaction intermediates, producing undesired side products. Many supra-molecular hosts are water soluble while possessing a hydrophobic interior cavity,and the host interior presents a chemical environment to encapsulated gueststhat is dissimilar to water. Thus, water can be used as the bulk solvent while thereaction itself takes place within the inner phase of the host, where reaction con-ditions are more favorable.Enzyme mimicry under biologically relevant reaction conditions (e.g., water as

the solvent, physiological temperature, and pH) has been a long-standing goal ofsupramolecular chemistry, and many reviews have been published that summa-rize these efforts [23,25,27,29–33,35,38,54,84–87]. Likewise, conducting organicreactions in water using self-assembled micellar nanoreactors is a research areathat has received considerable interest, and several reviews have been pub-lished [20,37,88,89]. Because these excellent reviews are quite comprehensive,this section will discuss selected examples that illustrate how supramolecularcatalysis can improve reactions in water.

7.3.1Water-Soluble Nanoreactors

A substantial fraction of self-asssembled molecular hosts are soluble in waterand possess hydrophobic interiors. When the reactants and/or catalyst of anorganic reaction are encapsulated within a hydrophobic cavity, the molecularhost can act as a nanometer-sized reaction flask, bringing together reactants that


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1517.3 Reactions in Water

would otherwise be insoluble [31]. While many examples of supramolecularcatalysis in water now exist, the most practical and synthetically useful strategythat has emerged is the use of micellar hosts that spontaneously self-assemble inwater. Advantages of these systems over other water-soluble hosts include theirreliable self-assembly under a wide range of conditions, the commercial availa-bility and low cost of many micelle-forming surfactants, and wide range ofhydrophobic molecules that are encapsulated [20,37,88,89]. Micelles lack definedstructure compared to other supramolecular structures, which is responsible fortheir broad encapsulation behavior. A corresponding shortcoming of these sys-tems is that they do not produce confinement effects found in other host-catalyzed systems, such as shape-based substrate gating or the enforcement ofspecific substrate orientations.Kobayashi and coworkers have developed a number of useful reactions in

water using Lewis acid–surfactant-combined catalysts (LASCs). Crucial to thesereactions was the counterintuitive discovery that rare earth metal triflates arewater-compatible Lewis acid catalysts for the Mukaiyama aldol reaction, andthat water is in fact required for catalyst activitiy [90–92].This led to the discover of the prototypical LASC, scandium tris(dodecyl sul-

fate) (Sc(DS)3), in which the Lewis acidic scandium atom possesses ligands withsurfactant properties. While the LASC is soluble in water, it creates a hydrophobicenvironment for reactants that slows the rate of silyl enolate hydrolysis, a majordecomposition pathway in water. The Mukaiyama aldol reaction between silylenolates and aldehydes proceeds rapidly and in high yield using Sc(DS)3 as a cata-lyst in pure water as the solvent (Scheme 7.14) [93,94]. In addition to the afore-mentioned advantages of using water as the reaction solvent, this system allowsthe use of aqueous formaldehyde instead of gaseous or polymeric forms of thevaluable C1 electrophile, which is not possible under anhydrous conditions [91].

Scheme 7.14

Kobayashi and coworkers have disclosed several additional reactions that areamenable to LASC catalysis in water (Scheme 7.15). The three-component Man-nich reaction of amines, aldehydes, and silyl ketene acetals is catalyzed bySc(DS)3 and in higher yield by a related Cu(II) LASC, copper bis(dodecyl sulfate)(Cu(DS)2) [94,95]. A similar three-component Abramov-type reaction of amines,


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Scheme 7.15

aldehydes, and phosphite ester nucleophiles is catalyzed by Sc(DS)3 [96]. Conju-gate additions to electron-deficient olefins with beta-ketoester and indolenucleophiles in water using Sc(DS)3 as a catalyst were reported [97,98]. It isnoteworthy that these reactions are all operationally simple and conducted atambient temperature.Asymmetric reactions are also possible using LASC catalysis (Scheme 7.16).

The ring opening of meso-epoxides with aromatic amines, catalyzed by Sc(DS)3

Scheme 7.16


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and a chiral a bipyridine ligand, proceeded with high enantioselectivity [99].Asymmetric catalysis of the Mukaiyama aldol reaction was also achieved usingCu(DS)2, a chiral bisoxazoline ligand, and a Brønsted acid additive [93,100]. Inthis case, however, the enantioselectivity was modest.Lipshutz and coworkers have made important contributions by advancing a

series of designer surfactants that serve as nanoreactors for green, practical, andsynthetically useful reactions in water (Scheme 7.17) [88,89]. Central to the suc-cess of this research effort has been the design of surfactants that self-assembleto form nanoreactors with optimal properties for mediating organic reactions inwater. The size and morphology of particles formed by these surfactants werefound to be particularly important, with 50–100 nm diameter particles beingmost effective. The structures of surfactants TPGS-750-M and Nok were bothoptimized with this property in mind, and accordingly are the most effective forperforming reactions in water. It should also be noted that these surfactants areenvironmentally innocuous, being derivatives of nontoxic compounds vitamin Eand β-sitosterol [101,102].

Scheme 7.17


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These designer surfactants, particularly TPGS-750-M and Nok, have beenexplored extensively for performing organic reactions in water as the bulk reactionsolvent. All of the most common transition-metal-catalyzed reactions can be per-formed efficiently under micellar conditions, including olefin metathesis, Sonoga-shira coupling, Suzuki–Miyaura coupling, Heck coupling, Stille coupling, Miyauraborylation, and Buchwald–Hartwig amination (Scheme 7.18) [101–113].

Scheme 7.18


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Other indispensable organic transformations, such as amide formation,nucleophilic aromatic substitution, and nitroarene reduction, can also be per-formed in water under micellar conditions (Scheme 7.19) [114–116]. Excellentyields are obtained for each of these micellar reactions at room temperature,while many of the corresponding reaction run in organic solvent under con-ventional conditions require elevated temperatures. This is due to the highlocal concentration found within the micellar nanoreactors, which acceleratesreaction rates.

Scheme 7.19

Beyond the advantages of switching the reaction solvent to water, Lipshutzand coworkers have demonstrated that using micellar nanoreactors leads to dra-matic reductions in waste when compared to traditional methods. The E factors(the ratio of waste to product produced by a chemical product) [82] of somerepresentative reactions run under micellar and conventional conditions werecompared, showing that micellar reaction E factors were typically reduced by anorder of magnitude relative to conventional reactions. Finally, the aqueousreaction mixture left over after product extraction contains surfactant and cata-lyst, and can be recycled several times without detrimental effect on yield, fur-ther reducing the amount of generated waste [117]. Very recently, scientists atNovartis published an analysis of the environmental and economic benefits ofusing TPGS-750-M in water instead of conventional organic solvents for thekilogram-scale production of an Active Pharmaceutical Ingredient (API) [118].Although the exact nature of the API and intermediates had to be obscured dueto the commercial sensitivity of the project, the authors reported a 50% reduc-tion in the quantity of organic solvents used and a 50% reduction in the quantityof substrates and reagents.


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7.3.2Dehydration Reactions

Performing dehydration reactions in aqueous solvent is typically a challengingtask, due to either thermodynamic (such as forming an amide or ester throughcondensation) or kinetic factors (such as when a carbocation can undergo elimi-nation or nucleophilic attack by water). Counter to intuition, however, it is pos-sible to bias reactions toward dehydration products in pure water if the reactiontakes place within the hydrophobic interior of a supramolecular nanoreactor.In 2002, Kobayashi and coworkers reported that a Brønsted acid-functional-

ized surfactant acted as a catalyst for esterification of carboxylic acids and alco-hols in water as the sole solvent [119]. Run under conventional conditions,removal of water formed as a coproduct of this reaction is typically necessary tobias the equilibrium toward the desired ester and achieve high yields. Esterifica-tion is successful in water using a catalytic quantity of dodecylbenzenesulfonicacid (DBSA), a micelle-forming Brønsted acid (Scheme 7.20). This reaction islimited to reaction partners that are quite hydrophobic, which is necessary forthem to partition into the micelle interior. The inability for water to penetrateinto the micelle core alters the thermodynamics of the system, producing highyields of ester. A similar approach was successful with other dehydrationreactions, such as ether formation, thioether formation, and thioacetal forma-tion. Since this report, several micelle-mediated dehydration reactions have beenreported.

Scheme 7.20

A tetrahedral, self-assembled metal–organic cage (Ga4L6, where L is a bisbi-dentate organic ligand) developed catalyzes the monoterpene-like Prins cycliza-tion of citronellal, as reported by the Raymond and Bergman groups in2012 [120,121]. This cyclization proceeds through the intermediacy of a carboca-tion, which can be deprotonated to form an alkene product, or trapped withwater to form the corresponding diol (Scheme 7.21). When the reaction is


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Scheme 7.21

conducted in buffered acidic water, the diol is the major product, while thealkene product predominates when the reaction is catalyzed by encapsulationwithin the Ga4L6 assembly. This effect is also seen in the gold-catalyzed eneynecycloisomerization, which similarly proceeds through a cationic intermediate(Scheme 7.22). In this case, the gold catalyst, PMe3AuBr, produces a productresulting from water incorporation. When a gold catalyst encapsulated withinthe Ga4L6 assembly (PMe3Au

+ � Ga4L6, where � denotes encapsulation) is usedinstead, a formally dehydrated product is also produced. In both of these cases,rate of water addition is substantially decreased within the hydrophobic interiorof the supramolecular assembly, an effect that is responsible for the stabilizationof various water-sensitive species within the same host [122–126].

Scheme 7.22

Fujita and coworkers have reported the catalysis of the Knoevenagel condensa-tion by inclusion within a self-assembled metal–ligand cage (Pd6L4) bearing a12+ charge. Low catalyst loading (1 mol%) of the cage is sufficient to catalyzethe condensation of 2-naphthaldehyde with Meldrum’s acid in high yield in


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neutral water as the solvent (Scheme 7.23). The Pd2+ centers located near thecage openings stabilize the anionic reaction intermediates, increasing thereaction rate. Finally, the reaction product is too large to fit within the host cav-ity, facilitating catalytic turnover [127].

Scheme 7.23

Lipshutz and coworkers recently reported the gold(III)-catalyzed dehydrativecyclization of propargyl diols and propargyl amino acids in water under micellarconditions. When the equivalent reaction is conducted in organic solvent, acti-vated molecular sieves are added to remove water, which is generated as a stoi-chiometric by-product [128,129]. Using TPGS-750-M as a micellar host for thisreaction, the cyclization reaction proceeds smoothly, producing furan and pyr-role products in high yields (Scheme 7.24). No dehydrating agents are requiredto drive the reaction forward, despite the presence of a vast excess ofwater [130].

Scheme 7.24

7.4Catalyst/Reagent Protection

Catalyst and reagent stability is an important issue in many synthetic reactions,and the prevention of off-pathway decomposition is critical for achieving lowcatalyst loadings and good atom economy. Supramolecular encapsulation of areactive catalyst or reagent within a host cavity can protect it from detrimentalinteractions, providing longer catalyst lifetimes. This can produce higher yields


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7.4.1

1597.4 Catalyst/Reagent Protection

and allow lower catalyst loading, which is particularly important when consider-ing the low earth abundance of many precious metals used in catalysis.

Catalyst Protection

Manganese porphyrins are useful catalysts for the oxidation of unactivated C��Hbonds, but they rapidly decompose, limiting their synthetic utility. The decom-position occurs through a bimolecular mechanism, forming an oxo-bridged Mndimer (Mn-O-Mn). The supramolecular metal-ligand square published by Huppand coworkers binds a single Mn porphyrin molecule through pyridine-Zn asso-ciation (Scheme 7.11). The lifetime of the encapsulated Mn porphyrin isincreased by 18-fold, and the turnover numbers are increased 10–100-fold aswell. The stabilization is due to the suppression of the bimolecular decomposi-tion by supramolecular protection [75]. Similar stabilization of Co–porphyrincatalysts are provided by encapsulation in work reported by de Bruin and cow-orkers (Scheme 7.12).The Bergman and Raymond groups reported the isomerization of allyl alco-

hols (Scheme 7.25) is catalyzed by a ruthenium(II) catalyst encapsulated within aself-assembled metal–ligand cage Ga4L6 (Scheme 7.21) [131]. This reactionexhibits host-mediated size selectivity, substrate inhibition, and the reaction pro-ceeds in water. The catalyst lifetime is prolonged by encapsulation, and com-pared to the performance of the unencapsulated catalyst in organic solvent,encapsulation leads to higher turnover numbers.

Scheme 7.25

Protection of Water-Sensitive Reagents

An intriguing and surprising finding from the Lipshutz group is that their micel-lar systems allow for the generation and reaction of several moisture-sensitiveorganometallic reagents, even when water is the reaction solvent [102]. Negishi-like couplings between alkyl and aryl halides can be accomplished using zinc

7.4.2


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dust and a palladium catalyst under micellar conditions in water (Scheme 7.26).The water-sensitive organozinc reagent is formed in situ at the metal surface andthen partitions into the anhydrous micelle interior more rapidly that it can reactwith water. At this point, transmetallation to a less sensitive organopalladiumspecies occurs.

Scheme 7.26

This concept was extended to perform cuprate conjugate addition reactions.The reaction of alkyl halides with zinc dust forms organozinc species, whichundergoes transmetalation to form an organocopper species [132]. The organ-copper reagent undergoes conjugate addition to an enone, catalyzed by AuCl3 asa Lewis acid (Scheme 7.27). Remarkably, this reaction proceeds smoothly despitethe fact that the reaction must proceed through two water-sensitive intermedi-ates in water as the bulk solvent. An additional feature is that this chemistryproceeds at room temperature instead of the cryogenic temperatures often nec-essary for organocopper chemistry.

Scheme 7.27

7.5Tandem Reactions

Tandem reactions, in which multiple reaction events occur sequentially in a sin-gle reaction vessel, offer an appealing alternative to iterative chemical synthe-sis [133]. The isolation and purification of intermediate products is energyconsuming, produces large quantities of chemical waste, and costly, so tandemreactions are particularly desirable from a green chemistry standpoint. The exe-cution of tandem reactions is difficult because the conditions required for multi-ple reactions are often incompatible. It is possible to use supramolecularencapsulation as a tool to circumvent this problem by partitioning anincompatible reaction event into a host interior, where it will no longer interfere


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7.5.1

1617.5 Tandem Reactions

with other reactions. This approach is inspired by enzymatic catalysis, in whichincompatible reactions occur in active sites that are isolated from other reactionprocesses in solution. Even in vitro, extremely impressive tandem processes arepossible using enzymatic catalysis. For instance, the one-pot synthesis of the pol-yketide natural product enterocin from simple precursors benzoic acid andmalonyl-CoA was accomplished. The tandem process forms 10 C��C bonds,5 C��O bonds, and 7 stereocenters, is catalyzed by 12 purified enzymes, andproceeds in 25% overall yield [134].

Synthetic Tandem Reactions

An impressive three-reaction tandem process enabled by supramolecular encap-sulation was recently disclosed by the Nitschke group [135]. In this process,furan first reacts with singlet oxygen (photogenerated by methylene blue) toform an endoperoxide, which is converted to fumaraldehydic acid in a step cata-lyzed by encapsulation within a self-assembled metal–organic host. Finally, theproline-catalyzed aldol reaction between nitromethane and fumaraldehydic acidyields the final lactone product in 30% yield (Scheme 7.28). All reactants andcatalysts are present at the beginning of the reaction, which proceeds withoutany of the three reaction cycles interfering with each other. Not only does encap-sulation within the cage catalyze the endoperoxide rearrangement, but it alsosuppresses nonproductive reaction pathways that occur when the cage is absent.It is also noteworthy that the cage itself self-assembles in the reaction mixture,and that the process occurs in water.

Scheme 7.28

As described in Section 3.1, a large number of transition-metal-catalyzedreactions can be conducted in water within the hydrophobic core of a self-assembled micelle. Except for the catalysts and reagents, the conditions requiredare nearly identical for each reaction. The generality of these reaction conditionshas enabled the Lipshutz group to design several multireaction tandem processes


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in water, which proceed in a single reaction flask and require no purification ofintermediates [111,113,136]. For instance, the diamination of 1-iodo-4-bromo-benzene was accomplished by an initial installation of a carbamate group, fol-lowed by a subsequent coupling with a second carbamate (Scheme 7.29). Bothamination events are facilitated by the same catalyst, and the second reactionevent is conducted by simply adding the second carbamate and increasing thereaction temperature.

Scheme 7.29

Micellar conditions allow for the formation of C��C bonds using the Suzuki orSonogashira coupling of 1-iodo-4-bromobenzene can be followed by a Pd-catalyzed amination step, furnishing the difunctionalized product (Scheme 7.30).In this case, it is worth noting that the reactions proceed with good yields,despite requiring two different Pd catalysts for the two coupling steps.

Scheme 7.30

7.5.2Chemoenzymatic Tandem Reactions

The importance of enzymes in organic synthesis is growing [137–140], and giventhat enzymes are particularly suited for tandem processes, the use of supra-molecular encapsulation to enable chemoenzymatic tandem reactions under bio-logical conditions is desirable. Bergman and Raymond have reported two tandemchemoenzymatic systems involving a self-assembled metal–ligand host [141]. Inthe first example, the initial allenic ester or amide is hydrolyzed by an esterase orlipase, followed by allene hydroalkoxylation catalyzed by an encapsulated gold


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1637.5 Tandem Reactions

complex (Scheme 7.31). This one-pot process proceeds in water affords producttetrahydrofurans in high yield. Supramolecular encapsulation prevents unwantedinteractions between the gold catalyst and enzyme; in the absence of the host,both catalytic reactions are negatively impacted.

Scheme 7.31

A second chemoenzymatic tandem process involves an allyl alcohol isomeriza-tion catalyzed by an encapsulated Ru(II) catalyst followed by NADPH-dependentenzymatic reduction of the resulting aldehyde (Scheme 7.32). Overall, the pro-cess represents a formal alkene reduction. Cofactor regeneration was accom-plished by a second enzyme, allowing sodium formate to be the terminalreductant instead of the expensive NADPH. In tandem processes involving syn-thetic reactions, incorporating additional reaction cycles is extremely challeng-ing, if not impossible. In this example, however, the second cofactor recyclingenzyme was added without any change in reaction conditions. The design ofmore complex chemoenzymatic processes will no doubt be aided by supra-molecular substrate gating and other forms of reaction control [23,86] to mini-mize crosstalk between reaction cycles.

Scheme 7.32


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7.6Conclusion

Supramolecular catalysis is still in an early stage of development, and much workhas been dedicated to establishing proof-of-concept rather than developing prac-tical processes. However, the examples in this chapter demonstrate how supra-molecular binding can be applied as a tool to achieve reaction outcomes that aredesirable from a green chemistry standpoint. Indeed, the past decade has seenthe productive application of supramolecular binding and encapsulation towardsynthetically useful and green reactions, particularly in the area of micellar catal-ysis, directed C–H functionalization, and hydroformylation. As supramolecularchemistry concepts continue to be adopted by the wider synthetic community,further practical and green applications can be expected. Finally, although usingsupramolecular protection to enable tandem reactions is still a research area inthe earliest stages of development, it holds great potential for reducing the time,waste, and energy involved in chemical synthesis. Particularly if one considersthe integration of synthetic and enzymatic chemistry into chemoenzymatic tan-dem processes, it is now possible to imagine a truly ideal reaction process inwhich a desired product is made from simple reactants in a single operation atambient temperature using water as the solvent. Again, it will be the adoption ofthese concepts by the wider synthetic community that will lead to practical andimpactful new processes.

References

1 Anastas, P.T. and Warner, J.C. (1998) 9 Hof, F., Craig, S., Nuckolls, C., and Rebek,Green Chemistry: Theory and Practice, J. (2002) Angewandte ChemieOxford University Press, New York. International Edition in English, 41, 1488.

2 Lancaster, M. (2002) Green Chemistry: 10 Pedersen, C.J. (1998) Angewandte ChemieAn Introductory Text, Royal Society of International Edition in English, 27, 1021.Chemistry, Cambridge. 11 Pedersen, C.J. (1967) Journal of the

3 Wender, P.A. and Miller, B.L. (2009) American Chemical Society, 89, 2495.Nature, 460, 197. 12 Chakrabarty, R., Mukherjee, P.S., and

4 Wender, P.A., Verma, V.A., Paxton, T.J., Stang, P.J. (2011) Chemical Reviews, 111,and Pillow, T.H. (2007) Accounts of 6810–6918.Chemical Research, 41, 40–49. 13 Northrop, B.H., Zheng, Y.-R., Chi, K.-W.,

5 Lehn, J.M. (1990) Angewandte Chemie and Stang, P.J. (2009) Accounts ofInternational Edition in English, 29, Chemical Research, 42, 1554.1304. 14 Caulder, D. and Raymond, K. (1999)

6 Cram, D.J. (1988) Angewandte Chemie Journal of the Chemical Society, DaltonInternational Edition in English, 27, 1009. Transactions, 1999, 1185.

7 Lehn, J.M. (1985) Science, 227, 849. 15 Rebek, C.J. (1997) Chemical Reviews, 97,8 Nguyen, S., Gin, D., Hupp, J., and Zhang, 1647.X. (2001) Proceedings of the National 16 Saalfrank, R.W., Maid, H., and Scheurer,Academy of Sciences of the United States A. (2008) Angewandte Chemieof America, 98, 11849. International Edition in English, 47, 8794.


Cop

yrig

ht ©

201

7. J

ohn

Wile

y &

Sons

, Inc

orpo

rate

d. A

ll rig

hts

rese

rved

.

165References

17 Singh, N., Tena-Solsona, M., Miravet, J.F.,and Escuder, B. (2015) Israel Journal ofChemistry, 55, 711.

18 Ohmatsu, K. and Ooi, T. (2015)Tetrahedron Letters, 56, 2043–2048.

19 Leenders, S.H.A.M., Gramage-Doria, R.,de Bruin, B., and Reek, J.N.H. (2015)Chemical Society Reviews, 44, 433.

20 La Sorella, G., Strukul, G., and Scarso, A.(2015) Greem Chemistry, 17, 644.

21 Brown, C.J., Toste, F.D., Bergman, R.G.,and Raymond, K.N. (2015) ChemicalReviews, 115, 3012.

22 Assaf, K.I. and Nau, W.M. (2015)Chemical Society Reviews, 44, 394.

23 Zarra, S., Wood, D.M., Roberts, D.A., andNitschke, J.R. (2014) Chemical SocietyReviews, 44, 419.

24 Yang, C. and Inoue, Y. (2014) ChemicalSociety Reviews, 43, 4123.

25 Raynal, M., Ballester, P., Vidal-Ferran, A.,and van Leeuwen, P.W.N.M. (2014)Chemical Society Reviews, 43, 1734.

26 Raynal, M., Ballester, P., Vidal-Ferran, A.,and van Leeuwen, P.W.N.M. (2014)Chemical Society Reviews, 43, 1660.

27 Kataev, E.A. and Müller, C. (2014)Tetrahedron, 70, 137.

28 Hapiot, F., Bricout, H., Menuel, S., Tilloy,S., and Monflier, E. (2014) CatalysisScience and Technology, 4, 1899.

29 Marchetti, L. and Levine, M. (2011) ACSCatalysis, 1, 1090.

30 Dong, Z., Wang, Y., Yin, Y., and Liu, J.(2011) Current Opinion in Colloid andInterface Science, 16, 451.

31 Yoshizawa, M., Klosterman, J.K., andFujita, M. (2009) Angewandte ChemieInternational Edition in English, 48, 3418.

32 Koblenz, T.S., Wassenaar, J., and Reek,J.N.H. (2008) Chemical Society Reviews,37, 247.

33 Oshovsky, G.V., Reinhoudt, D.N., andVerboom, W. (2007) Angewandte ChemieInternational Edition in English, 46, 2366.

34 Wilkinson, M., van Leeuwen, P., andReek, J. (2005) Organic and BiomolecularChemistry, 3, 2371.

35 Vriezema, D., Aragones, M., Elemans, J.,Cornelissen, J., Rowan, A., and Nolte, R.(2005) Chemical Reviews, 105, 1445.

36 Lutzen, A. (2005) Angewandte ChemieInternational Edition in English, 44, 1000.

37 Dwars, T., Paetzold, E., and Oehme, G.(2005) Angewandte Chemie InternationalEdition in English, 44, 7174.

38 Breslow, R. (1995) Accounts of ChemicalResearch, 28, 146.

39 Lehn, J.M. (1994) Applied Catalysis A,113, 105.

40 Uemura, T., Yanai, N., and Kitagawa, S.(2009) Chemical Society Reviews, 38,1228.

41 Ma, L., Abney, C., and Lin, W. (2009)Chemical Society Reviews, 38, 1248.

42 Lee, J., Farha, O.K., Roberts, J., Scheidt,K.A., Nguyen, S.T., and Hupp, J.T. (2009)Chemical Society Reviews, 38, 1450.

43 Suslick, K.S., Bhyrappa, P., Chou, J.-H.,Kosal, M.E., Nakagaki, S., Smithenry,D.W., and Wilson, S.R. (2005) Accountsof Chemical Research, 38, 283.

44 Kesanli, B. and Lin, W. (2003)Coordination Chemistry Reviews, 246,305.

45 Lensen, D., Vriezema, D.M., and vanHest, J.C.M. (2008) MacromolecularBioscience, 8, 991.

46 Helms, B., Liang, C.O., Hawker, C.J., andFrechet, J.M.J. (2005) Macromolecules,38, 5411.

47 Liu, L., Rozenman, M., and Breslow, R.(2002) Journal of the American ChemicalSociety, 124, 12660.

48 Liu, L. and Breslow, R. (2002) Journal ofthe American Chemical Society, 124,4978.

49 Chi, Y., Scroggins, S.T., and Fréchet,J.M.J. (2008) Journal of the AmericanChemical Society, 130, 6322.

50 Liu, L. and Breslow, R. (2003) Journal ofthe American Chemical Society, 125,12110.

51 Diederich, F. and Felber, B. (2002)Proceedings of the National Academy ofSciences of the United States of America,99, 4778.

52 Hoveyda, A.H., Evans, D.A., and Fu, G.C.(1993) Chemical Reviews, 93, 1307–1370.

53 Rousseau, G. and Breit, B. (2011)Angewandte Chemie InternationalEdition in English, 50, 2450.

54 Breslow, R. (1980) Accounts of ChemicalResearch, 13, 170.

55 Breslow, R. and Maresca, L.M. (1978)Tetrahedron Letters, 19, 887–890.


Cop

yrig

ht ©

201

7. J

ohn

Wile

y &

Sons

, Inc

orpo

rate

d. A

ll rig

hts

rese

rved

.


56 Breslow, R. and Maresca, L.M. (1977)Tetrahedron Letters, 18, 632–626.

57 Breslow, R. and Winnik, M.A. (1969)Journal of the American ChemicalSociety, 91, 3083.

58 Breslow, R., Zhang, X., and Huang, Y.(1997) Journal of the American ChemicalSociety, 119, 4535.

59 Das, S., Incarvito, C.D., Crabtree, R.H.,and Brudvig, G.W. (2006) Science, 312,1941.

60 Frost, J.R., Huber, S.M., Breitenlechner,S., Bannwarth, C., and Bach, T. (2014)Angewandte Chemie InternationalEdition in English, 54, 691–695.

61 Kuninobu, Y., Ida, H., Nishi, M., andKanai, M. (2015) Nature Chemistry, 7,712.

62 Maturi, M.M. and Bach, T. (2014)Angewandte Chemie InternationalEdition in English, 53, 7661.

63 Alonso, R. and Bach, T. (2014)Angewandte Chemie InternationalEdition in English, 53, 4368.

64 Müller, C., Bauer, A., and Bach, T. (2009)Angewandte Chemie InternationalEdition in English, 48, 6640.

65 Bauer, A., Westkämper, F., Grimme, S.,and Bach, T. (2005) Nature, 436, 1139.

66 Tan, K.L. (2011) ACS Catalysis, 1,877–886.

67 Yeung, C.S. and Dong, V.M. (2011)Angewandte Chemie InternationalEdition in English, 50, 809.

68 Lightburn, T.E., Dombrowski, M.T., andTan, K.L. (2008) Journal of the AmericanChemical Society, 130, 9210.

69 Grünanger, C.U. and Breit, B. (2008)Angewandte Chemie InternationalEdition in English, 47, 7346.

70 Joe, C.L. and Tan, K.L. (2011) Journal ofOrganic Chemistry, 76, 7590.

71 Worthy, A.D., Gagnon, M.M.,Dombrowski, M.T., and Tan, K.L. (2009)Organic Letters, 11, 2764.

72 Slagt, V.F., Reek, J., and Kamer, P. (2001)Angewandte Chemie InternationalEdition in English, 40, 4271–4274.

73 Slagt, V.F., van Leeuwen, P.W.N.M., andReek, J.N.H. (2003) Angewandte ChemieInternational Edition in English, 42, 5619.

74 Shenoy, S.R., Pinacho Crisóstomo, F.R.,Iwasawa, T., and Rebek, J. (2008) Journal

of the American Chemical Society, 130,5658.

75 Merlau, M., Mejia, M., Nguyen, S., andHupp, J. (2001) Angewandte ChemieInternational Edition in English, 40, 4239.

76 Lee, S.J., Cho, S.-H., Mulfort, K.L., Tiede,D.M., Hupp, J.T., and Nguyen, S.T.(2008) Journal of the American ChemicalSociety, 130, 16828.

77 Otte, M., Kuijpers, P.F., Troeppner, O.,Ivanovic ́ ́-Burmazovic , I., Reek, J.N.H.,and de Bruin, B. (2014) Chemistry – AEuropean Journal, 20, 4880.

78 La Sorella, G., Canton, P., Strukul, G.,and Scarso, A. (2014) ChemCatChem, 6,1575.

79 Trentin, F., Scarso, A., and Strukul, G.(2011) Tetrahedron Letters, 52, 6978.

80 La Sorella, G., Bazan, M., Scarso, A., andStrukul, G. (2013) Journal of MolecularCatalysis, 379, 192–196.

81 Breslow, R. (2013) Green Solvents:Reactions in Water, vol. 5, Wiley-VCH.

82 Sheldon, R.A. (2007) Greem Chemistry, 9,1273.

83 Butler, R.N. and Coyne, A.G. (2010)Chemical Reviews, 110, 6302.

84 Breslow, R. (1982) Science, 218, 532.85 Kirby, A. (1996) Angewandte Chemie

International Edition in English, 35, 708.86 Wiester, M.J., Ulmann, P.A., and Mirkin,

C.A. (2010) Angewandte ChemieInternational Edition in English, 50, 114.

87 Bistri, O. and Reinaud, O. (2015) Organicand Biomolecular Chemistry, 13, 2849.

88 Lipshutz, B.H. and Ghorai, S. (2012)Aldrichimica Acta, 45, 3.

89 Lipshutz, B.H. and Ghorai, S. (2008)Aldrichimica Acta, 48, 59.

90 Kobayashi, S. and Hachiya, I. (1992)Tetrahedron Letters, 33, 1625.

91 Kobayashi, S. and Hachiya, I. (1994)Journal of Organic Chemistry, 59,3590.

92 Kobayashi, S. and Nagayama, S. (1998)Journal of the American, 120, 8287–8288.

93 Kobayashi, S., Mori, Y., Nagayama, S.,and Manabe, K. (1999) Greem Chemistry,1, 175.

94 Manabe, K., Mori, Y., Wakabayashi, T.,Nagayama, S., and Kobayashi, S. (2000)Journal of the American ChemicalSociety, 122, 7202.


Cop

yrig

ht ©

201

7. J

ohn

Wile

y &

Sons

, Inc

orpo

rate

d. A

ll rig

hts

rese

rved

.

167References

95 Manabe, K.M. and Kobayashi, S. (1999)Organic Letters, 1, 1965–1967.

96 Manabe, K. and Kobayashi, S. (2000)Chemical Communications (Cambridge,UK), 669.

97 Mori, Y., Kakumoto, K., Manabe, K., andKobayashi, S. (2000) Tetrahedron Letters,41, 3107–3111.

98 Manabe, K., Aoyama, N., and Kobayashi,S. (2001) Advanced Synthesis andCatalysis, 343, 174–176.

99 Azoulay, S., Manabe, K., and Kobayashi,S. (2005) Organic Letters, 7, 4593.

100 Kobayashi, S., Nagayama, S., andBusujima, T. (1999) Tetrahedron, 55,8739–8746.

101 Klumphu, P. and Lipshutz, B.H. (2014)Journal of Organic Chemistry, 79, 888.

102 Lipshutz, B.H., Ghorai, S., Abela, A.R.,Moser, R., Nishikata, T., Duplais, C.,Krasovskiy, A., Gaston, R.D., andGadwood, R.C. (2011) Journal of OrganicChemistry, 76, 4379.

103 Lipshutz, B.H. and Abela, A.R. (2008)Organic Letters, 10, 5329.

104 Lipshutz, B.H. and Taft, B.R. (2008)Organic Letters, 10, 1329.

105 Nishikata, T. and Lipshutz, B.H. (2009)Chemical Communications (Cambridge,U.K.), 6472.

106 Nishikata, T., Abela, A.R., and Lipshutz,B.H. (2010) Angewandte ChemieInternational Edition in English, 49, 781.

107 Nishikata, T. and Lipshutz, B.H. (2010)Organic Letters, 12, 1972.

108 Lipshutz, B.H., Ghorai, S., Leong,W.W.Y., Taft, B.R., and Krogstad, D.V.(2011) Journal of Organic Chemistry, 76,5061.

109 Lipshutz, B.H., Isley, N.A., Moser, R.,Ghorai, S., Leuser, H., and Taft, B.R.(2012) Advanced Synthesis and Catalysis,354, 3175.

110 Isley, N.A., Gallou, F., and Lipshutz, B.H.(2013) Journal of the American ChemicalSociety, 135, 17707.

111 Isley, N.A., Dobarco, S., and Lipshutz,B.H. (2014) Greem Chemistry, 16, 1480.

112 Handa, S., Slack, E.D., and Lipshutz, B.H.(2015) Angewandte Chemie, 127, 12162.

113 Handa, S., Wang, Y., Gallou, F., andLipshutz, B.H. (2015) Science, 349,1087–1091.

114 Kelly, S.M. and Lipshutz, B.H. (2014)Organic Letters, 16, 98.

115 Gabriel, C.M., Keener, M., Gallou, F., andLipshutz, B.H. (2015) Organic Letters, 17,3968.

116 Isley, N.A., Linstadt, R.T.H., Kelly, S.M.,Gallou, F., and Lipshutz, B.H. (2015)Organic Letters, 17, 4734.

117 Bruce, H. and Lipshutz, S.G. (2014)Greem Chemistry, 16, 3660.

118 Gallou, F., Isley, N.A., Ganic, A., Onken,U., and Parmentier, M. (2016) GreemChemistry, 18, 14.

119 Manabe, K., Iimura, S., Sun, X.-M., andKobayashi, S. (2002) Journal of theAmerican Chemical Society, 124, 11971.

120 Hart-Cooper, W.M., Zhao, C., Triano,R.M., Yaghoubi, P., Ozores, H.L., Burford,K.N., Toste, F.D., Bergman, R.G., andRaymond, K.N. (2015) Chemical Science,6, 1383.

121 Hart-Cooper, W.M., Clary, K.N., Toste,F.D., Bergman, R.G., and Raymond, K.N.(2012) Journal of the American ChemicalSociety, 134, 17873.

122 Fiedler, D., Bergman, R.G., and Raymond,K.N. (2006) Angewandte ChemieInternational Edition in English, 45, 745.

123 Dong, V.M., Fiedler, D., Carl, B.,Bergman, R.G., and Raymond, K.N.(2006) Journal of the American ChemicalSociety, 128, 14464.

124 Brumaghim, J., Michels, M., andRaymond, K. (2004) European Journal ofOrganic Chemistry, 2004, 4552.

125 Brumaghim, J., Michels, M., Pagliero, D.,and Raymond, K. (2004) EuropeanJournal of Organic Chemistry, 5115.

126 Ziegler, M., Brumaghim, J., andRaymond, K. (2000) AngewandteChemie International Edition in English,39, 4119.

127 Murase, T., Nishijima, Y., and Fujita, M.(2012) Journal of the American ChemicalSociety, 134, 162.

128 Egi, M., Azechi, K., and Akai, S. (2009)Organic Letters, 11, 5002.

129 Aponick, A., Li, C.-Y., Malinge, J., andMarques, E.F. (2009) Organic Letters, 11,4624.

130 Minkler, S.R.K., Isley, N.A., Lippincott,D.J., Krause, N., and Lipshutz, B.H.(2014) Organic Letters, 16, 724.


Cop

yrig

ht ©

201

7. J

ohn

Wile

y &

Sons

, Inc

orpo

rate

d. A

ll rig

hts

rese

rved

.


131 Brown, C.J., Miller, G.M., Johnson, M.W.,Bergman, R.G., and Raymond, K.N.(2011) Journal of the American ChemicalSociety, 133, 11964.

132 Lipshutz, B.H., Huang, S., Leong,W.W.Y., Zhong, G., and Isley, N.A.(2012) Journal of the American ChemicalSociety, 134, 19985.

133 Fogg, D.E. and dos Santos, E.N. (2004)Coordination Chemistry Reviews, 248,2365.

134 Cheng, Q., Xiang, L., Izumikawa, M.,Meluzzi, D., and Moore, B.S. (2007)Nature Chemical Biology, 3, 557.

135 Salles, A.G., Zarra, S., Turner, R.M., andNitschke, J.R. (2013) Journal of theAmerican Chemical Society, 135, 19143.

136 Bhattacharjya, A., Klumphu, P., andLipshutz, B.H. (2015) Organic Letters, 17,1122.

137 Pàmies, O. and Bäckvall, J.-E. (2003)Chemical Reviews, 103, 3247.

138 Leresche, J. and Meyer, H. (2006) OrganicProcess Research and Development, 10,572.

139 Meyer, H. (2011) Organic ProcessResearch and Development, 15,180–188.

140 Clouthier, C.M. and Pelletier, J.N.(2012) Chemical Society Reviews, 41,1585.

141 Wang, Z.J., Clary, K.N., Bergman, R.G.,Raymond, K.N., and Toste, F.D. (2013)Nature Chemistry, 5, 100.


Cop

yrig

ht ©

201

7. J

ohn

Wile

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7 supramolecular catalysis as a tool for green...

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