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O
Br
CH O
Pd(O Ac)
2
(4 mo l%)
Bu
4
NBr, pyrrolidine
4A MS, DMF, 100 °C, 12 h
+
OH
OH
64%
Scheme 9.22 Example of acylation via arylation of enamine formed in situ in a
''phosphine-free'' system.
O
Cl
R'
Pd(db a)
2
(2 mol%), (
1
)
MS 4A, pyrro lidine
DMA, 140°C, 4 h
R'
CHO
+
R
R
OMe
N
(t-Bu)
2
P
(
1
)
Scheme 9.23 Arylation of enolizable aldehydes by aryl chlorides using Beller and co-
workers' phosphine ligand (1).
most reliable and wide-scope ''phosphine-free'' systems described so far for
deactivated aryl bromides.
With aryl chlorides the protocol is highly ligand dependent,
96
requiring
particular ligands of Beller and co-workers' phosphine series,
97
thus pro-
viding a useful versatile acyldechlorination method (Scheme 9.23).
9.1.3 Carbonylative and Decarbonylative Reactions
Carbonylative cross-coupling reactions are well known,
98
whereas their coun-
terpart in Heck chemistry has been elusive except for sporadic reports of
intramolecular examples.
99-101
On the other hand, a closely related dec-
arbonylative Heck reaction (Blaser reaction) is well known although still
rather unpopular in the synthesis and can involve aroyl chlorides,
102
but also
the respective anhydrides and p-nitrophenyl or enol esters,
103,104
the leaving
groups of which perform the role of base in the regeneration of Pd(0) spe-
cies, permitting rare cases of base-free (and potentially waste-minimized
105
)
Heck reactions.
The intermolecular carbonylative Heck reaction was reported by Miura
and co-workers,
106
but no protocol suitable for a wider range of substrates
was then elaborated. To discover appropriate conditions and catalytic sys-
tems in which sequential binding of carbon monoxide and olefin to an
arylpalladium intermediate can take place in the correct order is a chal-
lenging task. At least three competitive pathways can be identified in the
system involving CO (Scheme 9.24). Carbonylative and decarbonylative
pathways are intersected in the steps involving reversible binding/extrusion
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