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Anion radical coupling
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Plan
methods for the formation of aryl-aryl bonds
anionic cyclohydrogenation
history
mechanism
applications
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Selective formation of aryl-aryl bonds between reaction partners (no functionality other than C-H bonds at the
carbon atom):
transition metal catalyzed cross-coupling reactions
oxidative dimerization of electron-rich arenes (Scholl,
Kovacic and others)
intramolecular oxidative dimerization (Müllen)
oxidative photocyclization of stilbenes to phenanthrenes
(Mallory reaction)
thermal cyclodehydrogenations by flash vacuum pyrolysis
anionic cyclodehydrogenation of aromatic hydrocarbons
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Classic example of anionic cyclodehydrogenation:
Oxidative cyclization of 1,10-binaphthyl (1) to perylene (2)
M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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Anion radical coupling as an unique method
the highest efficiency in conversion 1,1’-binaphthyl to perylene
alkali metals are used to induce oxidation
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Classic example of anionic cyclodehydrogenation:
Oxidative cyclization of 1,10-binaphthyl (1) to perylene (2)
M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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History
• first isolated by Miller
• mechanism discovered by accident in 1967 by Solodovnikov et al.
Br
+ Li
3%
H.Gilman, C.G.Brennen, J. Am. Chem. Soc. 1949, 71, 657
M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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Definition
Aromatic radical anion
Ar + e- → Ar●-
Ar●- + e- → Ar2-
N. L. Holy, Chem. Rev. 1974, 74, 243
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General types of anion reactions
Ar + C C + Ar
D
Ar2- + C C + Ar
D
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General types of anion reactions
Ar + + Ar H
Ar2-
HB B-
+ HB B- + Ar H
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Reactivity of a radical anion
Compound Electron affinity[eV]
NaphthaleneTriphenylene
PhenantrhreneAnthracene
0,152 ± 0,0160,284 ± 0,0200,308 ± 0,0240,552 ± 0,061
N. L. Holy, Chem. Rev. 1974, 74, 243
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Mechanism
M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
The equilibrium constatnt depends on:
nature of the metal hydrocarbon solvent temperature
M + Ar → Ar●- + M+
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K, DME
M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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-
H Hpath A
-
e- e-
path B
-
-
H H
2-
M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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2- 2*-
[O] [O]
M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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Examined conditions
K (in an excess), THF, at 80 ºC gave 73% yield
Other conditions examined (metal, solvent, temperature) gave yelds of 10% or less:
a) K, 1,2-dimethoxyethane, 80 ºC
b) K, diglyme, 80 ºC
c) K, toluene, 80 ºC
d) Na, THF, 66 ºC
e) Na, diglyme, 80 ºC
f) Na, TMEDA, 120 ºC
g) Na, toluene, 110 ºC
M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358
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Oxidative agent
exposure to oxygene (small scale)
elemental iodine
Na2S2O5
SO2
S.H.Bossmann, H.Durr, M.R. Pokhrel, Synthesis 2005, 6, 907
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SO2 as an oxidative agent
N Na/THF
N-
N-
HH
Na+
Na+
SO2
N
N
49%
S. Hunig, I. Wehner, Synthesis 1989, 552
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Applications
P. Schlichting, U. Rohr, K. Müllen, J. Mater. Chem. 1998, 8, 2651
R
R
R
R
K, DME
R= C5H11
C6H13
C8H17
C12H25
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Applications
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Applications
Reductive ring closure of helicenes
K, THF
A. Ayalon, M. Rabinovitz, Tetrahedron Lett. 1992, 33, 17, 2395
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Applications
Terrylene synthesis
K, DME
U.Scherf, K. Müllen, Synthesis 1992, 23
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Summary
• formation of aryl-aryl bonds• efficiency• unique method• oxidazing agent• obscure mechanism
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Thank you !!!
Questions ???