Oxidation of benzylic alcohols with butyltriphenylphosphonium permanganate under non-aqueous conditions

Article abstract of DOI:10.1081/SCC-120015402

Oxidation of benzylic alcohols with butyltriphenylphosphonium permanganate (BuPh₃P⁺MnO₄^-) 1 (BTPPPM) in acetonitrile at room temperature is reported. This reagent selectively oxidizes benzylic alcohols in the presence of other oxidizable functional groups.

Full text of DOI:10.1081/SCC-120015402

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OXIDATION OF BENZYLIC ALCOHOLS WITH
BUTYLTRIPHENYLPHOSPHONIUM PERMANGANATE
UNDER NON-AQUEOUS CONDITIONS
Abdol Reza Hajipour a , Shadpour E. Mallakpour b & Heshmat A. Samimi a
a Pharmaceutical Research Laboratory , College of Chemistry , Isfahan University of
Technology , Isfahan, IR, 84156, Iran
b Pharmaceutical Research Laboratory , College of Chemistry , Isfahan University of
Technology , Isfahan, IR, 84156, Iran
Published online: 23 Aug 2006.
To cite this article: Abdol Reza Hajipour , Shadpour E. Mallakpour & Heshmat A. Samimi (2002) OXIDATION OF BENZYLIC
ALCOHOLS WITH BUTYLTRIPHENYLPHOSPHONIUM PERMANGANATE UNDER NON-AQUEOUS CONDITIONS, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 32:24, 3831-3838, DOI:
10.1081/SCC-120015402
To link to this article: http://dx.doi.org/10.1081/SCC-120015402
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Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
SYNTHETIC COMMUNICATIONS
Vol. 32, No. 24, pp. 3831–3838, 2002
OXIDATION OF BENZYLIC
ALCOHOLS WITH
BUTYLTRIPHENYLPHOSPHONIUM
PERMANGANATE UNDER
NON-AQUEOUS CONDITIONS
*
Abdol Reza Hajipour, Shadpour E. Mallakpour,
and Heshmat A. Samimi
*
Pharmaceutical Research Laboratory,
College of Chemistry, Isfahan University of
Technology, Isfahan 84156, IR, Iran
ABSTRACT
Oxidation of benzylic alcohols with butyltriphenylphospho-
nium permanganate (BuPh3PþMnO4À) 1 (BTPPPM) in aceto-
nitrile at room temperature is reported. This reagent
selectively oxidizes benzylic alcohols in the presence of other
oxidizable functional groups.
Oxidation of organic compounds in the absence of protic solvent is of
importance. This subject has been under intensive investigation in recent
years.[1–12] Along this line, we have introduced potentially oxidants in recent
years.[13–14] In this paper, we wish to report butyltriphenylphosphonium
*Corresponding authors. E-mail: haji@cc.iut.ac.ir
3831
DOI: 10.1081/SCC-120015402
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3832
HAJIPOUR, MALLAKPOUR, AND SAMIMI
permanganate (1) as a mild and novel oxidizing reagent for oxidation of
benzylic alcohols under non-aqueous conditions. This reagent is readily
prepared by the dropwise addition of an aqueous solution of KMnO4 to
an aqueous solution of butyltriphenylphosphonium bromide in quantitative
yield at room temperature.
The oxidation of alcohols with 1 (BTPPPM) proceeds under non-
aqueous conditions. The effects of various solvents such as Et2O, CH2Cl2,
THF, CHCl3, and CH3CN on the oxidation of sec-phenethyl alcohol with 1
were examined. TLC were used to monitor the rate of the oxidation. Only
acetonitrile was a suitable solvent for this oxidation system (Table 1).
Oxidation of sec-phenethyl alcohol to its corresponding ketone with
different amount of reagent 1 in acetonitrile were also examined (Table 2).
The reaction of 0.5 molar ratio of this reagent in compare to 1 molar ratio
proceeds with lower yield and even with longer reaction times (Table 2). The
optimum molar ratio of substrate to oxidant (1 : 0.8) is found to be ideal for
complete oxidation of alcohols. Secondary benzylic alcohols 2 are oxidized
to the corresponding ketones 3 in acetonitrile in excellent yields; benzoin
was also converted to benzil after 15 min at room temperature in acetonitrile
Table 1. Oxidation of sec-Phenethyl Alcohol with
Reagent 1 in Different Solvents at Room Temperature
Time
(min)
Entry
Solvent
Yieldb (%)
1
2
3
4
5
Et2O
THF
CH2Cl2
CHCl3
CH3CN
30
30
15
15
10
6
0
60
80
80
100
aOxidant/Alcohol (1 : 1).
bMonitored by TLC analysis.
Table 2. Oxidation of sec-Phenethyl Alcohol with Different Molar Ratio of
Reagent 1 in Acetonitrile at Room Temperature
Molar Ratio of Reagent 1
Reaction time (min)
Yielda (%)
1.0
10
100
0.8
15
100
0.7
30
80
0.5
30
60
aMonitored by TLC analysis.

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OXIDATION OF BENZYLIC ALCOHOLS
3833
in quantitative yield (Sch. 1 and Table 3). Oxidation of cinnamyl alcohol
with this reagent resulted in the cleavage of C¼C bond and converted
to benzaldehyde (60%) and cinnamaldehyde (40%). In comparison to
secondary benzylic alcohols, oxidation of aliphatic alcohols with this reagent
Scheme 1.
Table 3. Oxidation of Alcohols 2 with Reagent 1 to Carbonyl
Compounds 3 in Acetonitrile at Room Temperaturea,b
Time
(min)
Yieldc
(%)
Compound
R1
R2
2a
2b
2c
2d
2e
2f
4-PhC6H4
2-Pyridyl
C6H5
C6H5
C6H5
4-BrC6H4
4-ClC6H4
C6H5
a-Tetralol
Cyclohexanol
C6H5(CH2)2
C6H5(CH2)3
4-PhC6H4
3,4-(MeO)2C6H3
C6H5
Me
C6H5
C6H5CH2
Me
C6H5
Me
Me
C6H5CO
—
—
H
H
H
H
H
H
H
H
H
H
15
20
10
15
20
15
15
15
15
60
6
98
95
98
90
98
97
91
100
100
0
2g
2h
2i
2j
2k
2l
d 0
d 0
0
0
6
2m
2n
2o
2p
2q
2r
2s
2t
15
20
15
15
15
15
15
15
100d
90d
100d
90d
4-MeC6H4
2-MeC6H4
3-BrC6H4
4-ClC6H4
2-ClC6H4
90d
90d
100d
100d
aConfirmed by comparison with authentic samples (IR, TLC, and
NMR).[1–14]
bOxidant/Alcohol (0.8 : 1).
cYield of isolated pure product after chromatography or distillation.
dConversion monitored by TLC analysis.