Aerobic Oxidation of Alcohols Catalyzed by Iron or Vanadium Compounds - Transition Metal Catalysis in Aerobic Alcohol Oxidation - page 163

O

OH

1 mol% VO(acac) 2 , 3Å MS, O 2
MeCN, 80 o C

R 1

R 1

R 2

R 2

d n 4 r 4 n g | 5

Scheme 6.16 Aerobic oxidation of propargylic alcohols catalyzed by an oxovana-
dium complex.

VOX 2
A

OH

VO 2 X

H 2 O B

R

1/2 O 2

O

V

V(OH) 2 X HO O

X

D

R

O

C

R

Scheme 6.17 Plausible reaction mechanism for oxovanadium-catalyzed aerobic
oxidation of propargylic alcohols.

O

OH

CPVAP (30 mol% as V)

R 1 R 1

.

-PrCN, 100 o C, O 2 (1 atm) n

R 2 R 2

Scheme 6.18 Aerobic oxidation of propargylic alcohols catalyzed by a recyclable
vanadium complexes.

oxygen atmosphere. CPVAP can be readily separated by filtration and reused
at least 10 times without an appreciable decrease in catalytic activity.

6.2.3 Aerobic Oxidation of Allylic and Benzylic Alcohols
In 2007, Jiang and Ragauskas reported the vanadium-catalyzed selective
aerobic oxidation of activated alcohols (allylic and benzylic) in an ionic li-
quid solvent. The optimal conditions were treatment of the activated alco-
hols with 5 mol% VO(acac) 2 , 10 mol% DABCO (1,4-diazabicyclo[2.2.2]octane)
in [bmim][PF 6 ] (1-butyl-3-methylimidazolium hexafluorophosphate) at 80 1C
under an oxygen atmosphere (Scheme 6.19). 25 Several primary and second-
ary activated alcohols provided the corresponding aldehydes and ketones in
high yield. On the other hand, unactivated alcohols provided the carbonyl
compounds in poor yields. The catalysts can be recycled and reused for three
runs without any significant decrease in catalytic activity.