Overview: Representative Experimental Procedures, Comparative Tables and Conclusions - Transition Metal Catalysis in Aerobic Alcohol Oxidation - page 258

Representative procedure for the selective oxidation of unprotected diols. 2 To
a solution of alcohol (1 mmol) in dry CH 3 CN (1 mL) in a 20 mm culture
tube were added the following solutions: (1) Cu salt (0.05 mmol in 1 mL
CH 3 CN); (2) bpy (0.05 mmol in 1 mL CH 3 CN); (3) TEMPO (0.05 mmol in
1mLCH 3 CN); (4) base (0.1 mmol in 1 mL CH 3 CN). The reaction mixture
was stirred rapidly while open to air and monitored by TLC until no
starting material remained. The product was then worked up according to
one of the following two methods. Workup Method A. The reaction mixture
was neutralized with 1 N HCl and diluted with water (~10 mL) and
extracted with dichloromethane (3 20 mL). The combined organics were
washed with brine, dried over Na 2 SO 4 and concentrated. The crude
product was purified by silica gel column chromatography (gradient
elution of EtOAc in hexane). Workup Method B. The crude reaction mixture
was concentrated and purified by silica gel column chromatography
(gradient elution of EtOAc in hexane).

d n 4 r 4 n g | 6

10.3 Oxidation of Secondary Alcohols to Ketones
Iron- and ruthenium-based catalysts were reported to achieve this reaction in
a highly selective way. Oxidation of secondary alcohols in the presence of
primary alcohols, which were inert under the reaction conditions, was
reported using a binary Fe( III ) compound (see also Chapter 6, Scheme 6.1), 3
while a biomimetic bimetallic catalytic system composed of RuCl(OAc)(Ph 3 ) 3
in combination with hydroquinone and a cobalt-Schiff base complex led to
one of the fastest catalytic systems reported for the oxidation of secondary
alcohols (see also Chapter 3, Figures 3.1 and 3.2, and Chapter 7,
Equation 7.2). 4,5
However, the best optimized homogeneous procedures for the oxidation
of secondary alcohols employ palladium-based catalysts. Sigman and co-
workers developed three different Pd( II ) catalysts, 6 evaluated the substrate
scope and the reaction conditions of each of them in comparison studies
and concluded that the simple Pd(OAc) 2 -TEA system represents the most
convenient among the three, 7 as discussed in detail in Chapter 4 (Table 4.3).

.

Representative procedure for the Pd(OAc) 2 -TEA-catalyzed oxidation of
benzylic, secondary aliphatic and cyclic allylic alcohols. 7 To a 25 mL round-
bottomed flask equipped with a stir bar were added 6.7 mg of Pd(OAc) 2
(0.03 mmol, 0.03 equiv.) and 200 mg of powdered, freshly activated 3 Å
molecular sieves. To this were added 0.5 mL of THF, 2.83 mL of toluene
and 8.4 mL of TEA (0.06 mmol, 0.06 equiv.). A balloon of oxygen was at-
tached via a three-way joint. The flask was evacuated and refilled with
oxygen three times followed by vigorous stirring for 30 min at room
temperature under O 2 . To this solution 1 mmol of alcohol was added and
the mixture was stirred vigorously at room temperature under a balloon
of O 2 . The reaction progress was monitored by GC. After 12 h, the reaction