Anion radical coupling

Plan

methods for the formation of aryl-aryl bonds

anionic cyclohydrogenation

history

mechanism

applications

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

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

Anion radical coupling as an unique method

the highest efficiency in conversion 1,1’-binaphthyl to perylene

alkali metals are used to induce oxidation

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

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

Definition

Aromatic radical anion

Ar + e- → Ar●-

Ar●- + e- → Ar2-

N. L. Holy, Chem. Rev. 1974, 74, 243

General types of anion reactions

Ar + C C + Ar

D

Ar2- + C C + Ar

D

General types of anion reactions

Ar + + Ar H

Ar2-

HB B-

+ HB B- + Ar H

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

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+

K, DME

M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

-

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

2- 2*-

[O] [O]

M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

M. Rickhaus, A.P. Belanger, H. A. Wegner, L.T. Scott, J.Org.Chem. 2010, 75, 7358

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

Oxidative agent

exposure to oxygene (small scale)

elemental iodine

Na2S2O5

SO2

S.H.Bossmann, H.Durr, M.R. Pokhrel, Synthesis 2005, 6, 907

SO2 as an oxidative agent

N Na/THF

N-

N-

HH

Na+

Na+

SO2

N

N

49%

S. Hunig, I. Wehner, Synthesis 1989, 552

Applications

P. Schlichting, U. Rohr, K. Müllen, J. Mater. Chem. 1998, 8, 2651

R

R

R

R

K, DME

R= C5H11

C6H13

C8H17

C12H25

Applications

Applications

Reductive ring closure of helicenes

K, THF

A. Ayalon, M. Rabinovitz, Tetrahedron Lett. 1992, 33, 17, 2395

Applications

Terrylene synthesis

K, DME

U.Scherf, K. Müllen, Synthesis 1992, 23

Summary

• formation of aryl-aryl bonds• efficiency• unique method• oxidazing agent• obscure mechanism

Thank you !!!

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