Modern Heck Reactions - New Trends in Cross-Coupling: Theory and Applications - page 458

OMe H

COOH

NTs

Pd Cl 2 (10 mol% )
AgOTf (20 mol%)
DMSO-DMF, 80°C

+

MeO OMe F 3 C

OMe NHTs

MeO OMe CF 3

73%

Scheme 9.171 Example of decarboxylative hydroarylation of imines.

Ar CO OH
Pd 2+

H +

Pd 2+

Pd + Z Z ZH

Ar Pd + H +

R R R

H
Z=O,NTs

H H

Ar Ar

Scheme 9.172 Carbopalladation of C=heteroatom bonds terminated by protolysis.

COOH

OMe

PhCH 2 CN
Pd (TFA) 2 (8 mol% )
6-Me-2,2'-bipy,H 2 O
100°C, 48 h

MeO OMe

O

Ph
73%

OMe

Ar Ar Ar

ArPd(LL) +

H 2 O

N N O

R N

R Pd(LL) R H R

Scheme 9.173 Decarboxylative arylation of C N triple bonds.

co-workers, 447 to mention only a few examples to show that this extension of
the Heck pathway bears a huge potential for development.
Larhed and co-workers extended the method to C N triple bonds and
used this methodology to develop a new method of ketone synthesis by
decarboxylative carbopalladation of nitriles by electron-rich acids using 2,2 0 -
bipyridyls as ligands and excess nitrile as solvent (Scheme 9.173). 448 Primary
adducts, imines and their palladium derivatives were observed by ESI mass
spectrometry of the reaction mixtures.
An interesting reaction indirectly related to the topic under consideration
is the decarboxylative cross-coupling of cinnamic acid with aryl iodides re-
ported by Wu and co-workers. 449 The reaction is synthetically equivalent to
the archetypal Mizoroki-Heck reaction of aryl iodides with styrene. The
protocol shows that decarboxylative processes are not limited to particularly
substituted benzoic acids, although the reaction with cinnamic acids re-
quires harsh conditions and a special phosphine ligand. Ligands of this sort
were designed by Buchwald and co-workers for carrying out C-C, C-N, C-O
and other cross-coupling reactions with less reactive electrophiles (aryl and