Chemistry Reference
In-Depth Information
further range of derivatives can be obtained. Thus, for example, alcohols and
amines can be used for the preparation of esters and amides. Tsuji et al.
reported the preparation of esters as early as 1980.
88
The reaction proceeded
readily at ambient temperature under balloon pressure of CO.
More recently, Gabriele et al. reported the synthesis of 2-ynamides.
89
Initial attempts to use the conditions described by Tsuji et al. were in-
effective with amines, but under more forcing conditions reasonable prod-
uct yields (50-75%) were obtained for a variety of alkyl- and arylacetylenes
(Scheme 10.72). Effective reaction was limited to nucleophilic secondary
amines, hindered amines being unreactive and primary amines yielding a
complex mixture of products.
The Tsuji-Trost reaction, i.e. palladium-catalysed substitution at allylic car-
bon, has been widely applied in synthetic chemistry owing to the high level of
control over chemo-, regio- and steroeselectivity.
90
Normally, some function-
ality at the allylic reaction site is required, so the extension of this methodology
to C-H compounds is particularly useful. Progress in this direction was re-
ported by Jiang and co-workers, where alkenyl carboxylate esters were obtained
by oxidative alkoxycarbonylation (Scheme 10.73).
91
Benzoquinone was the
preferred oxidant with an additive, 2,3-dichloro-5,6-dicyanobenzoquinone
(DDQ), required to limit the second carboxylation to the diester.
The availability of a carboxylate directing group in a,b-unsaturated carb-
oxylic acids also allowed the formation of
cis-1,2-dicarboxylic acids
(Scheme 10.74).
92
The assistance of coordinating functions in stabilizing the interaction of
the C-H bond with the palladium centre is often crucial to achieving effec-
tive reaction. Many examples of this approach have been reported in the
PdI
2
(0.2 mol%)
KI (2 mol%)
R=
n
-Bu, R' = Et 54%
R=Ph,R'=Et 73%
R=Ph,R'=
n
-Bu
O
CO/air 4/1 (20 atm)
100 °C, Dioxane
R
+R
2
NH
62%
NR'
2
R
Scheme 10.72 Oxidative aminocarbonylation of 1-alkynes.
Pd(OAc)
2
(10 mol%)
BQ (2 equiv)
DDQ (0.5 equiv)
CH
3
CN, 50 °C
H
OMe
R'
+CO+MeOH
R'
(1 atm)
R"
O
R"
R=Ph, 77%
R=4-C
6
H
4
CF
3
47%
R=4-C
6
H
4
OMe
75%
R=2-C
6
H
4
Me
77%
Scheme 10.73 Oxidative allylic carbonylation of alkenes.
Pd(OAc)
2
(10 mol%)
Ag
2
CO
3
(2 equiv)
K
2
HPO
4
(1 equiv)
CO (1atm)
Dioxane, 110 °C, 12 h
H
COOH
COOH
COOH
H
H
Ph
Ph
Scheme 10.74 Oxidative carboxylation of an a,b-unsaturated carboxylic acid.
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