visible light photoredox catalysis in organic chemistry
TRANSCRIPT
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Visible Light Photoredox Catalysis in Organic Chemistry !
~Toward Green & Efficient Reactions~!DAMITH PERERA!
DEPARTMENT OF CHEMISTRY!
MICHIGAN STATE UNIVERSITY!
18 JANUARY, 2012!
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Photoredox Reaction: A Most Recent Example !
26-W light source
Ir(ppy)3 (0.5-1.0 %)NaOAc, DMA
23oC, 12 h
N R3R2
R1
CN
CN
N
R3
R2
R1 CN
+
α-aryl amine
IrNN
N
Ir(ppy)3
“Discovery of an alpha-Amino C–H Arylation Reaction Using the Strategy of Accelerated Serendipity” !
McNally, A.; Prier, C. K.; MacMillan, D. W. C.!Science 2011, 334, 1114-1117.!
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Photoredox Reaction: A Most Recent Example !
26-W light source
Ir(ppy)3 (0.5-1.0 %)NaOAc, DMA
23oC, 12 h
N R3R2
R1
CN
CN
N
R3
R2
R1 CN
+
α-aryl amine
IrNN
N
Ir(ppy)3
“Discovery of an alpha-Amino C–H Arylation Reaction Using the Strategy of Accelerated Serendipity” !
McNally, A.; Prier, C. K.; MacMillan, D. W. C.!Science 2011, 334, 1114-1117.!
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http://en.wikipedia.org/wiki/Serendipity!
Serendipity! !!• Serendipity: Fortunate Discoveries by Accident!
• Serendip, a former name for Sri Lanka + -ity.!
• In Science: !
“ It is true that my discovery of LSD was a chance discovery, but it was! the outcome of planned experiments and these experiments took place! in the framework of systematic pharmaceutical, chemical research. It! could better be described as serendipity ”!
! ! ! ! ! ! !- Albert Hofmann!!• Discovery of penicillin (Alexander Fleming) & cisplatin (Barnett Rosenberg)!
! !
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Accelerated Serendipity!
Choice of Catalysis: Photoredox Catalysis!
26-W light source
Ir(ppy)3 (0.5-1.0 %)NaOAc, DMA
23oC, 12 h
N R3R2
R1
CN
CN
N
R3
R2
R1 CN
+
α-aryl amine
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For an early discussion of visible light in photochemical reactions see Ciamician, G. Science 1912, 36, 385–394. ! !
Why Photoredox Catalysis? !
Visible Light (43% of Solar Energy): Readily available, clean and renewable.!!An attractive “reagent” for organic synthesis!!• Potential byproducts are minimized!• Atom economical!• Mild alternative to traditional methods!• Environmentally friendly!
! !
!Problem: Many organic molecules are unable to absorb! visible light requiring highly specialized energy !
! sources for traditional photochemistry!!Solution: Photoredox catalysis!
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McNally, A.; Prier, C. K.; MacMillan, D. W. C. Science 2011, 334, 1114-1117.!
Why Photoredox Catalysis? !
!“It is a relatively young and emerging field in organic synthesis that has recently delivered a variety of powerful bond-forming processes” !!
! ! ! ! ! -David MacMillan!
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Teply, F. Collect. Czech. Chem. Commun. 2011, 76, 859. !Narayanam, J. M. R.; Stephenson, C. R. J. Chem. Soc. Rev. 2011, 40, 102.!
Basics of Photoredox Catalysis!
Oxidative and Reductive quenching photoredox cycles of [Ru(bpy)3]2+!
Ru2+Ru3+strongoxidant
Ru+strong
reductant
3Ru2+
1Ru2+
hνφ = 0.042.12 eV
+0.84 V-0.83 V
hν
λmax452 nm
ηisc = 1
-1.33 V+1.29 V
reductive quenching
Et3N(CO2)2-
XanthateAscorbate
oxidative quenching
Ar-NO2Viologens
Fe3+
S2O82-
RuNN
N
N
N
N
tBu
tBu
tBu
tBu
tBu
tBu
(PF6)2
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History of Photoredox Catalysis !
1978! 1984! 2003! 2008!
Hedstrand D. M., Kruizinga W. H., Kellogg R. M. Tetrahedron Lett. 1978, 19, 1255.!
O
S+Ph
N
EtOOC COOEtO
SPh
BF4–
[Ru(bpy)3]Cl2 1 mol%CD3CN
25 ºC, room light0.3 h
++
quantatitive
Kellogg
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History of Photoredox Catalysis !
1978! 1984! 2003! 2008!
O
S+Ph
N
EtOOC COOEtO
SPh
BF4–
[Ru(bpy)3]Cl2 1 mol%CD3CN
25 ºC, room light0.3 h
++
quantatitive
Kellogg
N2+
COOH
BF4–
COOH
R
hν λ > 410 nm[Ru(bpy)3]Cl2
5 mol%
quantatitive
DeronzierCH3CN
R= H, Br or OMeR
Cano-Yelo H., Deronzier A. J. Chem. Soc., Perkin Trans. 2 1984, 1093.!
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History of Photoredox Catalysis !
1978! 1984! 2003! 2008!
Zen J. M., Liou S. L., Kumar A. S., Hsia M. S. Angew. Chem. Int. Ed. 2003, 42, 577!
Kellogg!Reduc&on Chemistry
SMe
R
S
R
Ovisible light500W halogen lamp
NPycx-Ru(bpy)
MeCN-H2O 3:4O2, pH = 1
3 h
R = H >97% R = COMe 96%
Zen
N2+
COOH
BF4–
COOH
R
hν λ > 410 nm[Ru(bpy)3]Cl2
5 mol%
quantatitive
DeronzierCH3CN
R= H, Br or OMeR
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History of Photoredox Catalysis !
1978! 1984! 2003! 2008!
Ischay M. A., Anzovino M. E., Du J., Yoon T. P. J. Am. Chem. Soc. 2008, 130, 12886.!
SMe
R
S
R
Ovisible light500W halogen lamp
NPycx-Ru(bpy)
MeCN-H2O 3:4O2, pH = 1
3 h
R = H >97% R = COMe 96%
Zen
O
Ph
O
PhHH
HHO
Ph
O
Ph
[Ru(bpy)3]Cl2 5 mol%
MeCN, iPr2NEt
LiBF4, visible light
intramolecular 89%, >10:1 dr
Yoon
Kellogg!Reduc&on Chemistry
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Pioneers in Photoredox Catalysis!2008 Onwards!
Tehshik P. Yoon!University of Wisconsin!
!
David MacMillan!Princeton University!
Corey R. J. Stephenson !Boston University!
… and others!
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Outline!
v Applications:!! Trifluoromethylation of Drugs! Total Synthesis !!
v α-Amino C-H Oxidation to:! ! C-C bond formation! C-N bond formation! C-P bond formation!
!v Transformations:!! C-O to C-X ! C-X to C=O ! C-B to C-O! C-X to C-H! Tandem Reactions!
v Future Developments!
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NR2 R1
R3
NR2 R1
R3
CN
NR2 R1
R3
NR2 R1
R3
N
NR2 R1
R3
PNO2 R4 O R5R4
KCN
R5
HN R4R5 PO R5
R4H
CN
CN
CNAza-Henry Strecker
NO O
The Catalytic Oxidation of α-Amino C-H Bonds !
C-C bond ! ! C-N bond C-P bond!
NR2R1
R3
NR2R1
R3
NR2R1
R3+
H H
+Photoredox
Catalyst
householdlight bulb
Habstraction Nu
NR2R1
R3
Nu
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Condie A. G., González-Gómez J. C., Stephenson C. R. J. J. Am. Chem. Soc. 2010, 132, 1464.!
Oxidative Aza-Henry Reaction!
[Ir(ppy)2bpy]PF6 (1 mol%)
R4CH2NO2visible light
10-18 h
R2 NR1
O2NR3
R4
R2 NR1
R3
N
R2
R1
N
R2
R1
H N R2R1
N
R1
R2
NO2
Ir(II)Ir(III)*
Ir(III)
Photoredoxcyclehousehold
light bulb
1 2 3
4
5
O2
O2
HO O
NO
O
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Oxidative Aza-Henry Reaction!
[Ir(ppy)2bpy]PF6 (1 mol%)
R4CH2NO2visible light
10-18 h
R2 NR1
O2NR3
R4
R2 NR1
R3
N N
O2N OMe
N
O2N
OMeN
O2N Br
92% 96% 90% 93%
O2N
N
MeO
MeONCl
92% 95% 27%
O2N O2N
N
O2N
N
96%
O2N
Condie A. G., González-Gómez J. C., Stephenson C. R. J. J. Am. Chem. Soc. 2010, 132, 1464.!
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Rueping, M.; Zhu, S.; Koenigs, R. M. Chem. Commun. 2011, 47, 8679!
Oxidative Strecker Reaction!
N
CN
N
CN Me
N
CN
N
CN Br
97% 97% 84% 82%
OMe
N
CN
N
CN
88% 79%
N
CN
76%
Me
Ph
N PhN Ph
CN
[Ir(ppy)2bpy]PF6 ( 1 mol%)KCN (1.2 equiv), AcOH (5 equiv), MeCN
5 W fluorescent bulb, O2
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Oxidative Strecker Reaction: Aniline Derivatives!
[Ir(ppy)2bpy]PF6
KCN, AcOH, MeCN 5 W fluorescent bulb
air as oxidant
NAr
N Ar
R1
R2
R1
R2
CN
N
CN
N
CN
N
CN
82% 74% 78%
Ph N
CN
84%
N
CN
70%
Me
Rueping, M.; Zhu, S.; Koenigs, R. M. Chem. Commun. 2011, 47, 8679!
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Proposed Mechanism!
NAr' Ar
R +
NAr' Ar
R + H
NAr' Ar
R + NAr' Ar
RNAr' Ar
R +
–H+ –H+
–e–
–e–
1,2-H shift
–H
Rueping, M.; Zhu, S.; Koenigs, R. M. Chem. Commun. 2011, 47, 8679!
N PhN Ph
CN
[Ir(ppy)2bpy]PF6 ( 1 mol%)KCN (1.2 equiv), AcOH (5 equiv), MeCN
5 W fluorescent bulb, O2
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Freeman, D. B.; Furst, L.; Condie, A. G.; Stephenson, C. R. Org. Lett. 2012, 14, 94.!!
Oxidant: Oxygen vs BrCCl3!
R1 NR2
R3
HA
R1 NR2
R3
HBRuII/I
Reductive Quenching (vs. SCE)Ru(bpy)3Cl22+〈 / Ru(bpy)3Cl21+: +0.84 VRu(bpy)3Cl21+ / Ru(bpy)3Cl22+: -1.31 V
HA: pKa~ 40HA: BDE (C-H) ~ 90.7 kcal/molEox (Et3N): +0.73 VHB: pKa~ 26.7HB: BDE (C-H) ~ 17 kcal/mol
H-atom abstraction
Deprotonation
R1 NR2
R3
R1 NR2
R3
[O]
[O2]
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Oxidant: Oxygen vs BrCCl3!
Freeman, D. B.; Furst, L.; Condie, A. G.; Stephenson, C. R. Org. Lett. 2012, 14, 94.!!
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Proposed Mechanism - First Hypothesis!
Freeman, D. B.; Furst, L.; Condie, A. G.; Stephenson, C. R. Org. Lett. 2012, 14, 94.!!
Ru(I)Ru(II)*
Ru(II)visiblelight
1 2 3
NAr N
ArH
R X
X + R
R H
N
Nu
Ar
N
NuAr
R X = BrCH(CO2Et)2,CCl4, BrCCl3
4
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Proposed Mechanism – Second Hypothesis!
Freeman, D. B.; Furst, L.; Condie, A. G.; Stephenson, C. R. Org. Lett. 2012, 14, 94.!!
Ru(I)Ru(II)*
Ru(II)visiblelight
1 2 3
NAr N
ArH
Br CCl3
NAr
H
CCl3 Br
3
NAr
4
NAr
5
NAr
Ionization
Br
CCl3
CCl3
electron transferBr CCl3
Br CCl3atom transfer
CHCl3Br
Initiation
Propagation
6
NAr
H
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Reactive Intermediate – Iminium ion !
Freeman, D. B.; Furst, L.; Condie, A. G.; Stephenson, C. R. Org. Lett. 2012, 14, 94.!!
1
NPh
2
NPh
Br
HA
Ru(bpy)3Cl2 (1 mol%)DMF, visible light, 1.5 hBrCCl3 (3 equiv)
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Trapping of Iminium With Other Nucelophiles!
Freeman, D. B.; Furst, L.; Condie, A. G.; Stephenson, C. R. Org. Lett. 2012, 14, 94.!!
Trapping of iminium intermediates
N N
O
O
Ph Ph
Ru(bpy)3Cl2 (1 mol %)BrCCl3 (3 equiv)
DMF, blue LEDs, 3 hthen no light
trimethylsiloxyfuran (5 equiv)(55% yield, d.r. 1:1)
N N
NH
Ph Ph
Ru(bpy)3Cl2 (1 mol %)BrCCl3 (3 equiv)
DMF, blue LEDs, 3 hthen no light
KOtBu (5 equiv)Indole (5 equiv)
(83% yield, d.r. 1:1)
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α-Amino Arylation!
26-W light source
Ir(ppy)3 (0.5-1.0 %)NaOAc, DMA
23oC, 12 h
N R3R2
R1
CN
CN
N
R3
R2
R1 CN
+
α-aryl amine
IrNN
N
Ir(ppy)3
McNally, A.; Prier, C. K.; MacMillan, D. W. C. Science 2011, 334, 1114-1117.!
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α-Amino Arylation!
CN
26-W light source
Ir(ppy)3 (0.5-1.0 %)NaOAc, DMA
23oC, 12 h
N R3R2
R1
CN
CN
N
R3
R2
R1 CN
+
α-aryl amine
IrNN
N
Ir(ppy)3
McNally, A.; Prier, C. K.; MacMillan, D. W. C. Science 2011, 334, 1114-1117.!
R2 NR1
R3 R2 NR1
R3
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Structural Scope !
CN
NPh CN
N
Me
MePh
N
CNRN
CNMeMeO
OMe
91% 94% R = Ph-4-Me - 93% Ph-4-F - 91% Ph-4-Br - 84% 2-Naphth - 81%
78%>20:1 r.r.
N
CNPh CN
NPh
CN
O
NPh CN
BocN
NPh
96% 98% 96% 95%
26-W light source
Ir(ppy)3 (0.5-1.0 %)NaOAc, DMA
23oC, 12 h
N R3R2
R1
CN
CN
N
R3
R2
R1 CN
+
α-aryl amine
IrNN
N
Ir(ppy)3
McNally, A.; Prier, C. K.; MacMillan, D. W. C. Science 2011, 334, 1114-1117.!
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Structural Scope !
NAr
X
CN
EWG
26 W fluorescent light bulb
Ir(ppy)3 (1.0 mol %)NaOAc, 23°C
DMA, 12 - 24 hamine arene
NAr
X
EWG
α - aryl amine
+
Electron-defficient arenes
NPh
NPh
NPh
NPh
NPh
NPh
CO2EtN
O
O
P OEtOEt
O
N NN
N CO2Et
NC
80% 64% 74%
44% 54% 70%
McNally, A.; Prier, C. K.; MacMillan, D. W. C. Science 2011, 334, 1114-1117.!
Electron-deficient arenes!
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Structural Scope !
NAr
X
CN
EWG
26 W fluorescent light bulb
Ir(ppy)3 (1.0 mol %)NaOAc, 23°C
DMA, 12 - 24 hamine arene
NAr
X
EWG
α - aryl amine
+
McNally, A.; Prier, C. K.; MacMillan, D. W. C. Science 2011, 334, 1114-1117.!
Electron-deficient heteroatomics
NNPh
NNPh
NNPh
NNPh
Me NH
NPh N
NNPh
NPh N
NMe
NPh N
X NPh N
NBoc
NN
O
OMe
Me
1: 72% 2: 87% 3: 26% 4: 61%
5: 49%6: 66%
7: X = O, 91%8: X = S, 79%
9: 92%
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Photoredox Arylation of Pharmaceuticals!
O N NO
O
NHAcF
O N NO
O
NHAcF
ON
Ir(ppy)2(dtbbpy)PF6(1 mol %)
26 W light bulb2-chlorobenzoxazole
NaOAc, 23°CDMA, 9 hZyvox (linezolid)
antibiotic 58%
McNally, A.; Prier, C. K.; MacMillan, D. W. C. Science 2011, 334, 1114-1117.!
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Xuan, J.; Cheng, Y.; An, J.; Lu, L.-Q.; Zhang, X.-X.; Xiao, W.-J. Chem. Commun. 2011, 47, 8337.!
Intramolecular C-N bond formation via photoredox!
R
TsHN N Ar2
Ar1 N
NTs
RAr1
Ar2
Ru(bpy)3Cl2(1 mol%)
5.0 equiv. tBuOK, MeOH, O236 W florescent light
48-72 h
NAr2 R
HNAr1 Ts
NAr2 R
HNAr1 Ts
NAr2 R
HNAr1 TsN
NR
Ar1
Ts
Ar2
H
reductivequench
Ru(I)
Ru(II)
Ru(II)*
[O]
[O]visiblelight
[OH] -
Base
intramolecularcyclization
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Intramolecular C-N bond formation via photoredox!
TsHN N Ar2
Ar1 N
NTs
Ar1
Ar2
Ru(bpy)3Cl2(1.0 mol% )
5.0 equiv. tBuOK, MeOH, O236 W florescent light
48-72 hPh
Ph
N
NTs
Ph
Ph
Ph
N
NTs
Ph
92%dr 10:1
93%dr > 19:1
Ph
N
NTs
Ph
OPh
90%dr > 19:1
92%dr > 19:1
N
NTs
Ph
Ph
ON
NTs
Ph
ClPh
N
NTs
Ph
BrPh
92%dr > 19:1
92%dr 8:1
Xuan, J.; Cheng, Y.; An, J.; Lu, L.-Q.; Zhang, X.-X.; Xiao, W.-J. Chem. Commun. 2011, 47, 8337.!
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Intramolecular C-N bond formation via photoredox!
R
TsHN N Ph
Ph N
NTs
RPh
Ph
Ru(bpy)3Cl2(1 mol%)
5.0 equiv. tBuOK, MeOH, O236 W florescent light
48-72 h
N
NTs
Ph
Ph
Ph
N
NTs
Ph
PhN
NTs
Ph
Ph
92%dr 10:1
92%dr > 19:1
89%dr 3:1
N
NTs
Ph
Ph94%
dr > 19:190%
dr 2:1
N
NTs
Ph
Ph
HN
NTs
Ph
Ph
SMe
45%dr 3:1
Xuan, J.; Cheng, Y.; An, J.; Lu, L.-Q.; Zhang, X.-X.; Xiao, W.-J. Chem. Commun. 2011, 47, 8337.!
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Proposed Stereochemical Pathways!
NAr2 R
HNTsAr1
NAr2 R
HNTsAr1
NAr2 R
NTsAr1 N
NR
Ar1
Ts
Ar2
NAr2 R
HNTsAr1
NAr2 R
NTsAr1 N
NR
Ar1
Ts
Ar2
KOBut HOButvisiblelight
Re-facefavoured
Si-facedisfavoured
Xuan, J.; Cheng, Y.; An, J.; Lu, L.-Q.; Zhang, X.-X.; Xiao, W.-J. Chem. Commun. 2011, 47, 8337.!
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Rueping, M.; Zhu, S.; Koenigs, R. M. Chem. Commun. 2011, 47, 8679.!
Photoredox catalyzed C–P bond forming reactions!
NR2
R1
R1
PO
R3
R3H
NR2
R1
R1
PR3
R3
O
[Ir(ppy)2bpy]PF6 (1 mol%)
1 mL toluene/water5 W lamp
0.1 mmol 3 equiv.
N
HH
89%
POEtOEt
O
N
HH
90%
POPhOPh
O
Br
N
HH
72%
POPhOPh
O
OMe
N
HH
73%
POPhOPh
O
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Outline!
v Applications:!! Trifluoromethylation of Drugs! Total Synthesis !!
v α-Amino C-H Oxidation to:! ! C-C bond formation! C-N bond formation! C-P bond formation!
!v Transformations:!! C-O to C-X ! C-X to C=O ! C-B to C-O! C-X to C-H! Tandem Reactions!
v Future Developments!
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Photocatalytic Alcohol Activation !
Dai, C.; Narayanam, J. M. R.; Stephenson, C. R. J. Nat. Chem. 2011, 3, 140-145.!Le´onel, E., Paugam, J. P.; Ne´de´lec, J.-Y. J. Org. Chem. 1997, 62, 7061. !
R OH R Br
Fe (2.5 equiv.), Cu (1.5 equiv.)CuBr (2.5 mol%), phenantroline (5 mol%)
CBr4 (2.0 equiv.), DMF
OH BrRu(bpy)3Cl2 (1.0 mol%)
CBr4 (2.0 equiv.) DMF, blue LEDs25 ºC, 5h, 70%
with NaBr(additive) : 90%
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Photocatalytic Alcohol Activation: Substrate Scope !
Dai, C.; Narayanam, J. M. R.; Stephenson, C. R. J. Nat. Chem. 2011, 3, 140-145. !
R2
R1 OH
Ru(bpy)3Cl2 (1.0 mol%)CBr4 (2.0 equiv.) or CHI3 (2.0 equiv.)
NaBr (2.0 equiv.) or NaI (2.0 equiv.) DMF, blue LEDs, 25-30 ºC, 5-15h, 70%
R2
R1 X(X= Br) or (X= I)
MeO
Br BrBnONTs
BrNTs
Br
BrNHCbz MeO
O
NHCbz HO
Br
OMeBr
O
Br
I
CbzHN I I
92% 95% 75%
84%
86%
75%
86%
83% 81%
90% 78% 77%
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Mechanistic Investigations !
Observations: Premature quenching primary alcohols leads to formate-ester side products !!!Hypothesis: DMF is involved in the transformation via in-situ formation of a Vilsmeier-Haak type reagent !!! N
H Br
Vilsmeler-Hack reagent!
OH OCHORu(bpy)3Cl2 (1.0 mol%)
(2 eq) CBr4, NaBr
DMF, blue LEDsRT, 24h: 92%
Dai, C.; Narayanam, J. M. R.; Stephenson, C. R. J. Nat. Chem. 2011, 3, 140-145. !
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Mechanistic Investigations !
Observations: Premature quenching primary alcohols leads to formate-ester side products !!!Hypothesis: DMF is involved in the transformation via in-situ formation of a Vilsmeier-Haak type reagent !!!
OH BrO DNHCbz
Ru(bpy)3Cl2 (1.0 mol%)CBr4 (2.0 equiv.)
DMF-d7, blue LEDs25 oC, 4 h
NHCbzNHCbz
O
(60%)
OH OCHORu(bpy)3Cl2 (1.0 mol%)
(2 eq) CBr4, NaBr
DMF, blue LEDsRT, 24h: 92%
Dai, C.; Narayanam, J. M. R.; Stephenson, C. R. J. Nat. Chem. 2011, 3, 140-145. !
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Mechanistic Investigations !
BrBrBr
BrDMF
Ru(bpy)33+
Ru(bpy)32+·
Ru(bpy)32+
OxidativeQuenching
Cycle
VisibleLight
CBr4
N
O Br
BrBr
Radical 7
N
O Br
BrBrBr
BrBrBr
Br
CBr4
DMF COBr2
Path B: AttackOf Bromide
Path A: AttackOf Alcohol
N
BrVilsmeier-Haack
Reagent 9
N
O HR
Br
Iminium 10
R OH
R BrR O H
O
H2O
Dai, C.; Narayanam, J. M. R.; Stephenson, C. R. J. Nat. Chem. 2011, 3, 140-145. !
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Aerobic Oxidation of Benzyl Halides!
Su, Y. J.; Zhang, L. R.; Jiao, N. Org. Lett. 2011, 13, 2168.!
Ar R Ar R
X OPhotocatalysis
Organocatalysis
AirSunlight
Ar R
Ru(bpy)3Cl2 (0.5 mol%)4-Methoxypyridine (20 mol%)
Li2CO3 (1 equiv)DMA, air, 9 h
sunlight
X
Ar R
O
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Aerobic Oxidation of Benzyl Halides!
Ar R
Ru(bpy)3Cl2 (0.5 mol%)4-Methoxypyridine (20 mol%)
Li2CO3 (1 equiv)DMA, air, 9 h
sunlight
X
Ar R
O
COOEt
O
X=Br, 75%
COOiPr
O
X= Br, 83%
COOCl
O
X= Br, 85%
O
O
X= Cl, 81%X= Br, 81%
O O
OO
O
F F
X= Br, 56% X= Cl, 39% X= Br, 0%
Su, Y. J.; Zhang, L. R.; Jiao, N. Org. Lett. 2011, 13, 2168.!
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Aerobic Oxidation of Benzyl Halides!
Su, Y. J.; Zhang, L. R.; Jiao, N. Org. Lett. 2011,13, 2168.!
Ar R
Ru(bpy)3Cl2 (0.5 mol%)4-Methoxypyridine (20 mol%)
Li2CO3 (1 equiv)DMA, air, 9 h
sunlight
X
Ar R
O
1a 2a
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Photoredox Hydroxylation of Arylboronic Acids!
Zou, Y.-Q.; Chen, J.-R.; Liu, X.-P.; Lu, L.-Q.; Davis, R. L.; Jørgensen, K.A.; Xiao. W.-J. Angew. Chem. Int. Ed. 2012, 51, 3!
Ar BOH
OHAr OH
[Ru(bpy)3Cl2] • 6H2O (2 mol%)R3N (2.0 equiv), DMF, air
visible light
RuIIRuI
RuII
[O2]
O2
Ar–OH
NR3
NR3
Visible light
Ar BOH
OH
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Photoredox Hydroxylation of Arylboronic Acids!
Ar BOH
OHAr OH
[Ru(bpy)3Cl2] • 6H2O (2 mol%)iPr2EtN (2.0 equiv), DMF, air
visible light24-32 h
OHMeO
OH
OH
OMe
OH
OH OH OH
OHPh
81% 94% 91% 72%
93% 72% 94% 69%
B[Ru(bpy)3Cl2] • 6H2O (2 mol%)iPr2EtN (2.0 equiv), DMF, air
visible light19 h
O
OOH
94%
Zou, Y.-Q.; Chen, J.-R.; Liu, X.-P.; Lu, L.-Q.; Davis, R. L.; Jørgensen, K.A.; Xiao. W.-J. Angew. Chem. Int. Ed. 2012, 51, 3!
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Mechanistic Insight!
RuII RuI
RuII
[18O2]
18O2
Visible
light
Ar B(OH)2
18O 18O
ArB(OH)2Ar B(O)2
18O 18OH
NEt2
H
BOH
OH18OArAr18OHhydrolysis
–18OH–
NEt3
NEt3
Zou, Y.-Q.; Chen, J.-R.; Liu, X.-P.; Lu, L.-Q.; Davis, R. L.; Jørgensen, K.A.; Xiao. W.-J. Angew. Chem. Int. Ed. 2012, 51, 3!
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Photoredox-mediated reductive dehalogenation!
Narayanam, J. M. R.; Tucker, J. W.; Stephenson, C. R. J. J. Am. Chem. Soc. 2009,131, 8756.!
NN
Br
HBoc
Boc NN
H
HBoc
Boc
A. Ru(bpy)3Cl2 (1 mol %)iPr2NEt/HCO2H (10 equiv)
DMF, visible light
orB. Ru(bpy)3Cl2 (1 mol %)
iPr2NEt (2.0 equiv)Hantschz Ester (1.1 equiv)
DMF, visible light
NN
Br
BocCO2Me
CO2MeH
HO N
OMe
O
Bn
OTBS
MeHO N
O
Ph
O
Bn
OH
H
O Ph
H
OI O
OPh
HO
I
O
H
Ph
92% A 79% A 80% A
89% B 81% B 88% B
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Mechanism!
Narayanam, J. M. R.; Tucker, J. W.; Stephenson, C. R. J. J. Am. Chem. Soc. 2009,131, 8756.!
Ru(bpy)32+* Ru(bpy)3+
Ru(bpy)32+
Photoredoxcycle
visiblelight
R1
X
R2
R1 R2
NEt
MeMe Me
MeHbHaCO2H N
Et
MeMe Me
MeHbHaCO2H Path B
Major
Path AMinor
R1
Ha
R2
R1
Hb
R2
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Photoredox [3+2] Cycloaddition/Aromatization!
Zou, Y.-Q.; Lu, L.-Q.; Fu, L.; Chang, N.-J.; Rong, J.; Chen, J.-R.; Xiao, W.-J. Angew. Chem., Int. Ed. 2011, 50, 7171!
N OEt
O
[RuI][RuII]*
[RuII]O2
O2Visiblelight
N
HOEt
O
1a I HO O
N
HOEt
O
II
H2O2
N OEt
OEWG EWG
[3+2]Cycloaddition
III
NCO2Et
EWG
EWG
NCO2Et
EWG
EWGOxidative
Aromatization
[O]
3
2
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Photoredox [3+2] Cycloaddition/Aromatization!
Zou, Y.-Q.; Lu, L.-Q.; Fu, L.; Chang, N.-J.; Rong, J.; Chen, J.-R.; Xiao, W.-J. Angew. Chem., Int. Ed. 2011, 50, 7171!
N OEt
O
1a
NO O
Ph
NCO2Et
3a
2a
(1) [Ru(bpy)3Cl2] (5 mol %) visible light, CH3CN, air
12 h
(2) NBS (1.1 equiv.), 1 h NO
O Ph
yield: 91%
NCO2Et
CO2Me
CO2Me
NCO2Et
NO
O Ph
12 h, 94% 22 h, 65%
NCO2Et
NO
O Ph
24 h, 93%
MeO
MeO
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Photoredox [3+2] Cycloaddition/Aromatization!
Zou, Y.-Q.; Lu, L.-Q.; Fu, L.; Chang, N.-J.; Rong, J.; Chen, J.-R.; Xiao, W.-J. Angew. Chem., Int. Ed. 2011, 50, 7171!
• Lamellarin alkaloids, a new family of marine natural products! !• Contain a pyrrolo[2,1-a] isoquinoline core!
N
O
O
MeO OAc
MeO
MeO
lamellarin D triacetate
Inhibitor of human topoisomerase I
MeO
AcO
N
O
O
MeO OSO3Na
MeO
MeOMeO
HO
lamellarin 20-sulfate
Inhibition of HIV integrase
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Radical Cation Diels-Alder Cycloadditions!
EDG
R
R
Visible lightRu(bpz)3(BArF)2
(0.5 mol%)
air, CH2Cl2r.t.
EDG
RR
MeMe
Me Me
MeO
1, 91%, 2 h
Me
MeO
Me Me
TBSO
Me
MeOPh
2, 72%, 20 h>10:1 endo:exo
Me
4, 77%, 4 h
Me Me
3, 88%, 1.5 h
NMeMe
Me5, 65%, 24 h
Ischay, M. A.; Fry, C. G.; Yoon, T. P. J. Am. Chem. Soc. 2011,133 ,19350!
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Radical Cation Diels-Alder Cycloadditions!
MeO MeORu(bpz)3(BArF)3
hν, CH2Cl2, air
MeO MeO
Ru(bpz)32+
Ru(bpz)3+
Ru(bpz)32+
O2O2
hν
MeO
MeO
Ischay, M. A.; Fry, C. G.; Yoon, T. P. J. Am. Chem. Soc. 2011,133 ,19350!
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Heitziamide A: A Case for Photoredox D.A.!O
O
NH
O
Heitziamide A
O
O
HN
O
myrcenefagaramide
O
O
NH
O
150 ºC2:1 trans:cis
60%
thermal regioisomer
O
O
OTBS
O
O
OTBSmyrcene
Ru(bpz)3(PF6)2 (2 mol%)visible light, air, CH2Cl2
80%
steps
+
Ischay, M. A.; Fry, C. G.; Yoon, T. P. J. Am. Chem. Soc., 2011, 133 ,19350!
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Radical Anion Hetero-Diels-Alder Cycloadditions!
Hurtley, A. E.; Cismesia, M. A.; Ischay, M. A.; Yoon,T. P. Tetrahedron 2011, 67, 4442.!
CORCOAr
O
H
HAr
OR
Ru(bpy)3Cl2 (5 mol%)
iPr2NEt, LiBF4
visible light, MeCN
Cl CF3 OAc
O
F
86 % 70% 83% 76%
77% 84% 6%
Ar = R =
Ar= Ph R= CH2OBn Ar= Ph R= t-Bu76% 12%
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Mechanism!
Path b
OMe
O[LA]
H
H
H
PhOPh
O[LA]
H
H
H
Me
Path a
or
4Favored
5Disfavored
Ru(bpy)3+
Ru(bpy)32+ ∗
Ru(bpy)32+
OxidativeQuenching
Cycle
VisibleLight (hν)
i-Pr2NEt
i-Pr2NEt
Me
Ph
O
O[LA]
[LA]-1
Me
Ph
O
O[LA]
2
+ [LA]
Me
Ph
O
O
1
Ph
O
H H
Me
O
3
[LA]
ba
i-Pr2NEtor
[LA-1]
OPh
OH
H
H
Me
6
Hurtley, A. E.; Cismesia, M. A.; Ischay, M. A.; Yoon,T. P. Tetrahedron 2011, 67, 4442.!
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Photoredox Radical Cyclization/Cope!
Tucker, J. W. ; Stephenson, C. R. J. Org. Lett. 2011, 13, 5468!
ArAr Br
O
N PG
IrIII*/II
40oC
Ar
N
O
R PG
ArN Ar
N
O
PGR
PG
O
R
radicalcyclization
Coperearrangement/rearomatization
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Combining Photoredox with Transition Metals!
N
H
H
+I
MesBF4
2.0 equiv
10 mol % Pd(OAc)2AcOH, Temp, 12 h
Temp = 100 οC: 60 % yieldTemp = 25 οC: 7 % yield
N
N
PdII
PdII
O
O
O
O IMes
BF4
+
Ratedetermining
stepN
N
PdIV
PdII
O
O
O
O
N2cat. Ru(bpy)3Cl2
hν-N2
25 οCCL
CHL
cat Pd(OAc)2
Kalyani, D.; McMurtrey, K. B.; Neufeldt, S. R.; Sanford, M. S. J. Am. Chem. Soc. 2011, 133, 18566!Kalyani, D.; Deprez, N. R.; Desai, L. V.; Sanford, M. S. J. Am. Chem. Soc. 2005, 127, 7330.!
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Combining Photoredox with Transition Metals!
N
R
R + [Ph-N2]BF4 N
R
R
Ph
10 mol% Pd(OAc)22.5 mol% Ru(bpy)3Cl2.H2O
26 W light bulbMeOH, 25 οC
N
Ph Ph
O
Me
N
O
76% 79%
N2
Me Ar
O
Me
N
O
87%
Kalyani, D.; McMurtrey, K. B.; Neufeldt, S. R.; Sanford, M. S. J. Am. Chem. Soc. 2011, 133, 18566!
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Mechanism!
CH3L + [Ar-N2]BF4 L C Ar
10 mol % Pd(OAc)22.5 mol % Ru(bpy)3Cl2.6H2O
26 W light bulbMeOH, 25 oC
Ru(bpy)33+
Ru(bpy)32+·
Ru(bpy)32+ *
VisibleLight
BF4 + N2 + Ar
[ArN2]BF4
LPdIV
C Ar
L C-H
L ArC+ HL
PdIIIC
LPdIII
C Ar
Ar
Kalyani, D.; McMurtrey, K. B.; Neufeldt, S. R.; Sanford, M. S. J. Am. Chem. Soc. 2011, 133, 18566!
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Outline!
v Applications:!! Trifluoromethylation of Drugs! Total Synthesis !!
v α-Amino C-H Oxidation to:! ! C-C bond formation! C-N bond formation! C-P bond formation!
!v Transformations:!! C-O to C-X ! C-X to C=O ! C-B to C-O! C-X to C-H! Tandem Reactions!
v Future Developments!
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Trifluoromethylation of Aldehydes!
Nicewicz D. A., MacMillan D. W. C. Science 2008, 322, 77.!
H
O
RI
F F
R1
Ir(ppy)2(dtbbpy)PF6 (0.5 mol%)DMF, organocatalyst 2 (20 mol%)
2,6-lutidine, -20 oC26 W fluorescent light bulb
H
O
R
F F
R1
NH
MeO
Me t-Bu
TFA
Organocatalyst 2(20 mol%)
IrN
NNN
t-Bu
t-Bu
Photocatalyst 1(0.5 mol%)
Catalyst Combination Photon Source
26 W fluorescentlight bulb
H
O
C6H13
H
O
CF3
H
O
C6H13
CF3 Ph
Me CF3
CF3F
H
O
C6H13
F
Br
F
79% yield, 99% ee 65% yield, >20:1 d.r., 99% ee 72% yield, 98% ee 68% yield, 99% ee
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Mechanism!
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Synthesis of α-Trifluoromethyl Carbonyl Compounds!
Access to novel CF3. synthons
R' CF3
R
O CF3R'
R
O
a-CF3 carbonyl carbonyl
R'R"
OR'
R"
OSIR3
R' CF3
O
R"
R3Si-X CF3I
in situ pre-generated
potocatalystweak light
carbonyl a-CF3 carbonyl
Nagib D. A.; Scott, M. E.; MacMillan D. W. C. J. Am. Chem. Soc. 2009, 131, 10875.!
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Trifluoromethylation of Ketone Silylenol Ethers!
R'R'"
R"
OSiR3[Ru(bpy)3]2+.H2O 0.5 mol%
26W fluorescent lamp
CF3IiPr2EtN, H2OTHF, 23oC
XCF3
R' R"
O
enolsilane a-CF3 ketone
[a] Yield of isolated product; SiR = TIPS unless otherwise noted. [b] TES ether employed. [c] TBS ether employed. [d] 2.2:1 d.r. [e] With NaHCO3 in MeCN and TES ether.
R
OCF3
R = 1: H 92% 2: OMe 78% 3: CN 66% 4: I 83% 5: Br 85% 6: Cl 85% 7: F 80%
X NR
O O O O
CF3CF3 CF3 CF3
Me MeMe1: 72%[b]
2: 74%[c,d]
3: X = O[e] 64%4: X = S[e] 72%
5: R = Boc[e]
73%6: R = Cbz[e]
59%
O CF3
7: 68%e
CF3
O8: 84%[b]
O
CF3
Me
9: 76%
Nagib D. A.; Scott, M. E.; MacMillan D. W. C. J. Am. Chem. Soc. 2009, 131, 10875.!
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Trifluoromethylation of Silylenolesters and Amides!
X R"
R'
OTBS
CF3I, DMF, 23oC26W fluorescent lamp
X CF3
R' R"
O
silylketeneacetal
a-CF3ester/amide
No photocatalyst!
O EtO CF3
n-hexyl
OOCF3
i-amyl-O
OCF3
Me Me
Me2N CF3
O
n-propyl
N CF3
O
Me Me
1: 85% 2: 86% 3: 74% [b,c]
4: 76% 5: 84% [b]
[a] Yield of isolated products. [b] 0.5 mol % 1.H2O, Et3N, isoamyl alcohol employed. [c] in MeCN.
Nagib D. A.; Scott, M. E.; MacMillan D. W. C. J. Am. Chem. Soc. 2009, 131, 10875.!
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Trifluoromethylation of Arenes and Heteroarenes
Unactivated arenes
HY
X
B
C
A
H
H Ru(phen)3 2+ (1-2%)CF3SO2Cl (1-4 equiv.)
K2HPO4, MeCN, 23oC26-W light source
Y
X
B
C
A
CF3
CF3 CF3
Nagib D. A.; Scott, M. E.; MacMillan D. W. C. J. Am. Chem. Soc. 2009, 131, 10875.!
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Trifluoromethylation of Arenes and Heteroarenes
Unactivated arenes
HY
X
B
C
A
H
H Ru(phen)3 2+ (1-2%)CF3SO2Cl (1-4 equiv.)
K2HPO4, MeCN, 23oC26-W light source
Y
X
B
C
A
CF3
CF3 CF3
*Ru(phen)32+
Reductant 2-0.90 V
Ru(phen)32+
photocatalyst 1
Photoredoxcatalysis
Ru(phen)33+
oxidant 3+ 1.31 V
Household light
S
O
O
ClF3C
CF3SO2Cl .-
-Cl-
-SO2
-0.18 V
H
R
Arene
CF3
HR
CF3
HR
CF3
R
CF3 Arene-H+
SET
SET
-0.1 V
FF
F
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Substrate Scope !
Nagib D. A.; Scott, M. E.; MacMillan D. W. C. J. Am. Chem. Soc. 2009, 131, 10875.!
O S
N
S O
NH N
Ac
CF3 CF3
CF3
CF3
CF3
CF3
H3C
H3C CH3
CH3CH3
1: 80% 2: 76% (3:1)*
3: 70% 4: 84%
5: 72% (4:1)* 6: 81% (3:1)*
NMe
CF3
NH
CF3 NH
CF3
S CF3O CF3
NBoc
CF3
F3C
Me Me
1: 94% 2: 78%
3: 88% 4: 91%
5: 87% 6: 82%
N
N
N
N
N
N
N
N
N
HN
N
N
N
N
N
N
N
N N
N
MeN
O O
CF3 CF3 CF3 CF3 CF3
CF3
CF3 CF3 CF3 CF3
CF3 CF3 CF3CF3 CF3
OMe
Me
Me Me Me Cl Cl Me Me
OMe
OHMe
MeMeS
Me OMe
OMeMeO
Me
Me Me
OMe
Me
OMe
O
O
Me
Me
O
Me Me
1: 82% 2: 78% 3: 94% 4: 70% 5: 73%
6: 74% 7: 85% 8: 72% 9: 86% 10: 81%
11: 78% (3:1)* 12: 78% 13: 87% 14: 90% 15: 88%
CF3 CF3 CF3 CF3 CF3
CF3 CF3 CF3 CF3 CF3
CF3 CF3 CF3 CF3 CF3
NHBoc OMe SMe Me
Me Me
MeBr
Me
Me
Me
MeMe
Me
MeO
MeO
O
O BF3K
Me
Me
MeO
OMe
Me3Si
OMe
Me
OMe
tBu
Me
1: 74% 2: 80% (3:1) 3: 84% (2:1) 4: 73% (2:1) 5: 70%
6: 75% (4:1) 7: 77% (2:1) 8: 72% (2:1) 9: 92% (5:1) 10: 74% (2:1)
11: 77% 12: 85% 13: 76% 14: 85% (4:1) 15: 78% (5:1)
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Applications to Existing Drug Molecules !Selectivity
N
NOO
O O OF3C
CF3CF3Me
Me
MeO
MeO
DNA base analogueCF3- methyluracil
92%
Anti-Alzheimer'sCF3- Ariccept precursor
94%
Vitamin PCF3- Flavone
85%
Promiscuity
H
OCF3
OMeOMe
MeOH
OMe
Me
CF3
Me
CF3
MeHN N
Me
MeO
Flavorant (coffee/chocolate)CF3-methylvanillin
82% (5:1)
Anti-inflammatoryCF3-ibuprofen78% (1.4:1)
Anaesthetic, anti-arrhythmicCF3-lidocaine
78% (2:1)
Nagib D. A.; Scott, M. E.; MacMillan D. W. C. J. Am. Chem. Soc. 2009, 131, 10875.!
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Applications to Existing Drug Molecules !
Nagib D. A.; Scott, M. E.; MacMillan D. W. C. J. Am. Chem. Soc. 2009, 131, 10875.!
NH
ON
OH OH O
OH
MeMe
F
Cholesterol-lowering drug Lipitor
4
2
4'
NH
ON
OH OH O
OH
MeMe
F
F3C
4 CF3- Lipitor27%
NH
ON
OH OH O
OH
MeMe
FF3C4' CF3- Lipitor
27%
NH
ON
OH OH O
OH
MeMe
F
CF3
2 CF3- Lipitor25%
CF3 -Lipitor74% yield
1:1:1 mixture of regioisomers
Seperation by SFC
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Total Synthesis of (+)-Gliocladin C!
Furst, L.; Narayanam, J. M. R.; Stephenson, C. R. J. Angew. Chem., Int. Ed. 2011, 50, 9655.!
!• Gliocladin C - cytotoxic against P-388 lymphocytic leukemia cell lines!
• C3–C3’ indole alkaloids, contain the 3a-(3-indolyl) hexahydropyrrolo-[2,3-b]indole skeleton!
NH
N
HN
N
O
O O
Me
H
3
3'2
Gliociadin C
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Total Synthesis of (+)-Gliocladin C!
Furst, L.; Narayanam, J. M. R.; Stephenson, C. R. J. Angew. Chem., Int. Ed. 2011, 50, 9655.!
NH
N
HN
N
O
O O
Me
H
10 steps
HN
CHO
NH
CO2Me
NHBoc Cl OEtO
O
MeNH2
Commercially available starting materials
NN
BrCOR
RR N
NCOR
RR N
NH
COR
RR
RuII*/I
blue lightirradiation
HN
R.
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Outline!
v Applications:!! Trifluoromethylation of Drugs! Total Synthesis !!
v α-Amino C-H Oxidation to:! ! C-C bond formation! C-N bond formation! C-P bond formation!
!v Transformations:!! C-O to C-X ! C-X to C=O ! C-B to C-O! C-X to C-H! Tandem Reactions!
v Future Developments!
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Future Developments !
Neumann, M.; Füldner, S.; König, B.; Zeitler, K.; Angew. Chem. Int. Ed. 2011, 50, 951.!
H
O
5+ I (CF2)2CF3
NH
NOMe
20 mol%
hv, LEDeosin Y 0.5 mol%
2,6-lutidine 1.4 eqDMF, -15 ºC, 18 h
H
O(CF2)2CF3
556%, 96% ee
.HCl
8 eq
H
O
5
85%, 88% ee
CO2Et
CO2Et
H
OH
O
Ph
CO2Et
CO2Et
O
NO2
85%, 88% ee 85%, 88% ee5
Use of the Organic Dyes!
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Use of Organic Dyes!
Hari, D. P.; Konig, B. Org. Lett. 2011, 13, 3852.!
N Ar
CH2(CN)2
Eosin Y(2 mol%) hn
R1CH2NO2
Eosin Y(2 mol%) hn
(R3O)2P(O)H
Eosin Y(2 mol%) hn
CH2(CO2R2)2
Eosin Y(2 mol%) hn
N
CNAr
82-93%
NAr
NO2R1
66-80%
NAr
CO2R2CO2R2
86-92%
N
P(OR)2Ar
82-93%
O
O
COOHBr
OBrBr
HO
Br
Eosin Y
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Conclusions!
• Generation of new C-C, C-N and C-P via α-Amino C-H Oxidation and mild alternative to existing methods. !
• Valuable functional group transformations.!
• Applications in Drug discovery and Total synthesis.!
!“and glass buildings will rise everywhere; inside of these will take place the photochemical processes that hitherto have been the guarded
secret of the plants, but that will have been mastered by human industry which will know how to make them bear even more abundant fruit than
nature”!!
! !! ! ! !! !Ciamician, G. Science 1912, 36, 385–394. !!
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Acknowledgements!
Dr. Maleczka !!
Dr. Borhan!!!
The Maleczka group!!
Luis, Rosario, Li, Fangyi, Peter, Susanne, Aaron and Hamid !!!
Anil, Munmun, Salinda, Udayanga and Dilini!!
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Thank you all !!!