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2 AcOH
+
OH
O
H
2
O
Pd
II
Co
1
OH
OAc
O
Pd
0
+ 2 H
+
O
2
Co
OAc
O
2
Scheme 7.3 Catalytic cycle of palladium-catalyzed biomimetic aerobic oxidation of
1,3-dienes.
RuCl(OAc)(PPh
3
)
3
-hydroquinone-Co(salophen)(PPh
3
) 6 at room temperature
under air afforded benzaldehyde (5) in 60% yield (Equation 7.2). Turnover
numbers (TONs) up to 70 were obtained and the system was ecient with
benzylic and allylic primary alcohols.
10
RuCl(OAc)(PPh
3
)
3
(1.2 mol %)
hydroquinone (3 mol %)
6
(2 mol %)
OH
O
air (1 atm), DCM, 20 °C
4
5
, 60 %
(7.2)
Me
N
N
N
Co
PPh
3
Co(salophen)PPh
3
(6)
O
O
The use of this methodology with secondary alcohol substrates required
careful optimization. The more challenging dehydrogenation step was ac-
complished using Shvo's catalyst 7,
11
a binuclear ruthenium complex, which
dissociated in solution into two complexes of Ru
II
(7a) and Ru
0
(7b)
(Scheme 7.4). Electron-rich 2,6-dimethoxybenzoquinone (8) was used to
Ph
O
H
O
P
h
Ph
P
h
Ph
Ph
OH
Ph
O
Ph
Ph
Ph
+
Ph
Ph
Ph
Ph
Ph
Ph
Ru
Ru
CO
Ru
Ru
H
OC
CO
OC
CO
H
CO
OC
CO
7
7a
7b
Scheme 7.4
Shvo catalyst 7.
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