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Pd(OTs)
2
(MeCN)
2
(5 mol%)
BQ (2 equiv)
p
-TsOH (0.5 equiv)
CO (1 atm)
CO
2
Me
R
3
NHCONR
1
R
2
H
THF/MeOH (1:1)
18 °C, 3 - 5 h
CH
2
Cl
2
, 18 °C, 3 - 5 h
R
3
NHCONR
1
R
2
O
Pd(OTs)
2
(MeCN)
2
(5 mol%)
BQ (2 equiv)
p
-TsOH (1 equiv)
CO (1 atm)
O
R
3
NR
1
R
2
N
Scheme 10.79 Oxidative carbonylation of arylureas.
Pd(OAc)
2
(10 mol%)
AgOAc (2 equiv)
TEMPO (2 equiv)
KH
2
PO
4
(2 equiv)
CO (1 atm)
Hexane
130 °C, 24 h
O O
NHC
6
F
5
S
O O
NHC
6
F
5
COOH
S
O
O
S
H
NC
6
F
5
Pd(OAc)
2
(10 mol%)
AgOAc (2 equiv)
KH
2
PO
4
(2 equiv)
CO (1 atm)
O
Scheme 10.80
Sulfonamide-drected oxidative carbonylation.
There is an evident need to maximize the selectivity of C-H activation to
ensure regioselectivity. Recently, Yu and co-workers studied the benefits of
sulfonamide as a directing group for a number of reactions, including car-
bonylation.
102
Reactions occurred exclusively at sites ortho to the sul-
fonamide group. Using Pd(OAc)
2
/AgOAc/KH
2
PO
4
/CO (1 atm) in n-hexane at
130 1C for 24 h, intramolecular ring closure occurred, and in the presence of
TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) the carboxylate product was
isolated (Scheme 10.80).
Examples of the use of hydroxyl functions as directing groups in C-H
carbonylation are less common, but Yu and co-workers illustrated that it is
possible to convert a-disubstituted phenethyl alcohols to 1-iso-
chromanones.
103
They found that it was necessary to add a protecting ligand
[the preferred example was (
þ
)-menthyl(O
2
C)-Leu-OH] to prevent palladium
black formation under the reductive CO atmosphere (Scheme 10.81). Pri-
mary and secondary phenethyl alcohols were unstable under the reaction
conditions, leading to reduced yields and oxidative decomposition products.
The carboxylation of anisoles was reported by Ishii and co-workers.
104
In
this case, molybdovanadophosphate was employed as the acid. With
Pd(OAc)
2
as catalyst, under 0.5 atm of CO and 0.5 atm of O
2
in acetic acid at
70 1C for 15 h, the major product was the para derivative with ortho sub-
stitution forming the minor product (
3 : 1 ratio).
The oxidative carbonylation of heteroarenes, and in particular N-substituted
indoles, to yield 3-substituted indole acids and esters was first reported in
B
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