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F
F
F
CF
3
F
CF
3
Pd(OAc)
2
(10 mol%), AgOAc (2 equiv)
TEMPO ( 2 equiv), KH
2
PO
4
(2 equiv)
CO (1 atm),
n
-hexene, 130 °C, 18 h
O
O
R
1
R
2
R
1
R
2
N
F
H
F
F
F
H
O
Scheme 10.85 Oxidative carbonylation of C
sp
3
-H in amides.
TBP
t
-BuO
PhCH
2
PhCH
3
PhCH
2
COO
t
-Bu
[Pd
0
]
PhCH
2
COOEt
major product
t
-BuOH
O
Single electron
transfer
PhCH
2
PdCO
t
-Bu
O
PhCH
2
PdCOEt
PhCH
2
PdO
t
-Bu
slow
CO
EtOH
fast
CO
PhCH
2
PdOEt
t
-BuOH
Scheme 10.86 Reaction mechanism for oxidative carbonylation of toluene.
work, reaction required the presence of ethene, presumed to act as a
hydrogen acceptor, and water, to activate the catalyst resting state. In a
substrate that offers the potential for either C
sp
2
-H or C
sp
3
-H conversion, the
former shows preferential reactivity.
118,119
Yu and co-workers also reported
on the carbonylation of C
sp
3
-H of amides leading to a range of succinimides
that could be further hydrolysed to provide 1,4-dicarbonyl compounds
(Scheme 10.85).
120
They found that the choice of TEMPO as co-oxidant (with
AgOAc) was crucial.
The reaction of C
sp
3
-H bonds in toluene derivatives was reported by Huang
and co-workers (Scheme 10.86).
121
In this case, the preferred oxidant was di-
tert-butyl peroxide, leading to a radical-involved benzylic C-H functionaliza-
tion. Carbonylation in the presence of ethanol as the preferred nucleophile led
to the synthesis of a range of ethyl 2-phenylacetate derivatives. Under opti-
mized conditions, turnover numbers 4100 were achieved. The absence of
product when the reaction is carried out in the presence of radical scavengers
such as TEMPO and 1,1-diphenylethylene suggests that activation of the
benzylic substrate by removal of a hydrogen atom to form a benzyl radical
precedes two-step oxidation of Pd(0) in a single electron transfer process.
10.6 Conclusion
Carbon-carbon and carbon-heteroatom bond formation using carbon
monoxide has been widely exploited in organic synthesis during the last
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