770 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 770±771$
Oxidation by Chemical Manganese Dioxide.
Part 3.1 Oxidation of Benzylic and Allylic Alcohols,
Hydroxyarenes and Aminoarenes$
Masao Hirano,*a Sigetaka Yakabe,a Hideki Chikamori,a
James H. Clarkb and Takashi Morimotoa
aDepartment of Applied Chemistry, Faculty of Technology, Tokyo University of Agriculture
and Technology (TUAT), Koganei, Tokyo 184-8588, Japan
bDepartment of Chemistry, University of York, Heslington, York YO1 5DD, UK
The combined use of chemical manganese dioxide (CMD) and molecular sieves in hexane (or in acetone) in general or
CMD alone in particular cases enables the convenient and efficient oxidation of benzylic and allylic alcohols, phenols
and amines under relatively mild conditions
We have recently reported in this journal on the use of
chemical manganese dioxide (CMD)2,3 for the oxidation
of a series of benzylic monoalcohols1a and thiols,1b and
the oxidative carbon±carbon bond cleavage of 1,2-diols,1a
in which molecular sieves (MS) served as the ecient
adsorbent of concomitantly formed water, allowing the easy
work-up of products to be performed. The CMD±MS
system leads to a selective and high-yielding oxidation, and
thus can favorably be compared to conventional active
manganese dioxide (AMD)-based oxidations.4 Further
studies have been performed in order to extend the scope
of the CMD-based reaction, since the development of a
new, convenient reagent system is invariably a fascinating
challenge.
Reactions were in general carried out simply by eciently
stirring a heterogeneous mixture of a substrate, CMD and
MS in gently re¯uxing hexane under an inert atmosphere.
Oxidations of benzenedimethanols and allylic alcohols
are illustrated in Scheme 1. Oxidation of benzene-1,2-
dimethanol 1a was slow and gave a mixture of phthalalde-
hyde 2a and phthalide 3 in low and moderate yield respec-
tively, even after prolonged reaction. In contrast, oxidation
of 1,3- 1b and 1,4-derivatives 1c proceeded smoothly and
produced isophthalaldehyde 2b and terephthalaldehyde 2c,
respectively, in essentially quantitative yields. The poor
reactivity of 1a towards CMD could therefore be explained
in terms of steric hindrance of the o-substituents as observed
in the oxidation of substituted benzylic alcohols with
CMD1a and also with AMD.5 trans-Cinnamyl alcohol 1d
was readily converted to cinnamaldehyde 2d without loss of
the double bond stereochemistry. The CMD±MS system
failed to bring about the selective oxidation of a polyene
Scheme 1 (No MS was added in the oxidation of 1e and 1f)
primary alcohol, nerol 1f, to the cis-aldehyde 2f, being
accompanied by the formation of an appreciable amount
sively. 1,4-Benzoquinones 4c±e can be obtained in excellent
yields from hydroquinones 3c±e. AMD oxidation of 3c gave
quinhydrone,6 a binary 1:1 complex derived from 3c and 4c,
in certain cases, but it was absent in the present reaction.
On the other hand, resorcinol 3b was inert under the
oxidation conditions used for 3a and 3c, the substrate being
recovered essentially unchanged. Phenols 3f and 3g under-
went p,p- and o,o-couplings easily to give the dipheno-
quinone 4f and the bisphenol 4g, respectively. In addition,
some aminoarenes 5a±d can successfully be oxidised with
the CMD±MS system (Scheme 3).
Although the CMD-based system requires elevated
temperature to achieve the reaction at a reasonable rate, it
can oxidise a number of functional groups in high yields.
Indeed, yields of unsaturated aldehydes, 2d (92%) and 2e
(96%), and the quinone 4c (96%), for example, are much
higher than those from typical AMD oxidations (Goldman's
procedure7 using azeotropically activated AMD in benzene,
of the trans-isomer 2e (>10%). Attempted oxidation using
CMD alone, however, was found to be eective for the
selective oxidation of 1f and also of geraniol 1e. The
absence of 1e from the reaction mixture of 1f coupled with
the fact that 2f is stable under the oxidation conditions
might imply that the isomerization occurs during the inter-
mediate stage of the oxidation under the in¯uence of MS.
Typical alicyclic 1g and aliphatic allylic alcohols 1h gave
unsaturated ketones in moderate to good yield.
Di- and mono-hydroxyarenes were then treated with the
CMD±MS system (Scheme 2). Oxidation of catechol 3a in
hexane gave a mixture of the o-quinone 4a and an unknown
product, but a repeat run in the acetone produced 4a exclu-
*To receive any correspondence. Fax: 81-423-88-7033.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).