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PdCl
2
(5 mol%)
CuCl
2
·2H
2
O
dioxane, 80°C
HO
+
CO
2
Me
CO
2
Me
86 %
Cl
CuCl
2
PdCl
2
Pd(OH)Cl
CO
2
Me
Pd Cl
HO
HO
Cl
PdCl
Cl
CO
2
Me
CO
2
Me
PdCl
ClP dH
HO
HO
Cl
Cl
Scheme 9.10 Example of alkenylation initiated by chloropalladation of an alkyne,
and mechanism (in dashed box).
Cl
Br
Pd(O Ac)
2
(5mol%)
LiCl, AcOH, r.t.
Ph
Br
+
Cl
Ph
80%
Scheme 9.11 Alkenylation initiated by chloropalladation: an example of the proto-
col developed by Zhu and co-workers.
70
AcO
Pd(O Ac)
2
(5 mo l%)
2,2 '-b ipyr idyl, AcOH, 80°C
OAc
94%
O
O
Scheme 9.12 Example of intramolecular alkenylation initiated by acetoxypalladation.
triple bond, corresponding to pathway E in Scheme 9.9.
72
Thus, the catalytic
cycle has a PdH complex at the beginning, being formed either spon-
taneously or by decarbonylation-elimination from isobutyryl chloride.
Regeneration of PdH at the end of each cycle makes this catalytic process
self-sustaining without bases, oxidants or any other reagents (Schemes 9.13
and 9.14).
Similar couplings were reported to be catalysed by Co,
73
Ni,
74
Ru
75
and
Rh,
76,77
although an alternative mechanism involving metallacycles is often
considered for such transformations.
9.1.2 Heck Reaction Versus Cross-Coupling
In palladium- and, more generally, transition metal-catalysed C-C bond
formation methodology, the Heck reaction is a major type of process,
compared with cross-coupling, in which a new C-C bond is formed by
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