Modern Heck Reactions - New Trends in Cross-Coupling: Theory and Applications - page 449

O O

Si(OMe) 3

Pd( OAc) 2 (5 mol%)
A gF (300 mol%), ai r
1,10-phen
DMF, 60°C

+

Ph

90%

Scheme 9.154 Desilylative arylation reaction using fluoride activation.

PhSnMe 3
PdCl 2 (5 mol%)
CuCl 2, THF, r.t., 2 h

MeO 2 C CO 2 Me

66%

MeO 2 C CO 2 Me

Ph Ph

PdCl 2

PhPdCl PhSnBu 3

PhSnBu 3

MeO 2 C CO 2 Me

Ph PdCl

Scheme 9.155 Alkyne diarylation via destannylative Heck reaction cascaded with
Stille cross-coupling.

only to standard olefins, but also to cyclohexenone (Scheme 9.154), acryla-
mide, vinyl acetate and 2-vinylpyridine. A similar system employing a less
common ligand, the bis(2-pyridylhydrazone) of glyoxal, was introduced by
Mino et al. 423

9.3.4 Destannylative Heck Reaction
The oxidative Heck reaction with organotin compounds was first performed
by Heck, who carried out a few runs with tetraphenyltin within studies on
organomercuric compounds. As the results were disappointing, tin com-
pounds were practically abandoned. Closely related is an alkyne diarylation
procedure developed by Kosugi and co-workers, who showed that the
reactivity of organotin compounds towards transmetallation allows trapping
of

the carbopalladation intermediate by the cascade cross-coupling

event (Scheme 9.155). 424 A similar diarylation procedure was used for

norbornene. 425
The first protocol for destannylative oxidative arylation was reported by
Mori and co-workers using Cu(II) as terminal oxidant to afford the expected
products in good yields, although the reaction required prolonged heating
(Scheme 9.156). 426
A major improvement was subsequently reported by Jung and co-workers,
who employed roughly the same system, but managed to perform the re-
actions at room temperature. 427 However, an even a more important advance
was the use of oxygen as the sole terminal reoxidant, which was shown to be
as effective as cupric salts and in some cases significantly more effective.
More recent reinvestigation of the behaviour of organotin compounds
under conditions of the oxidative Heck reaction was initiated by Sigman and