ORGANIC
LETTERS
1999
Vol. 1, No. 13
2129-2132
Chromium(VI) Oxide-Catalyzed Benzylic
Oxidation with Periodic Acid
Shigekazu Yamazaki
Toyama Industrial Technology Center, 150 Futagami, Takaoka,
Toyama 933-0981, Japan
Received October 22, 1999
ABSTRACT
CrO3 has been found to be an efficient catalyst for benzylic oxidation with periodic acid as the terminal oxidant in acetonitrile. Substituted
toluenes with an electron-withdrawing group at the 4- or 3-position and diarylmethanes such as diphenylmethane and fluorene were oxidized
to the corresponding substituted benzoic acids and ketones in excellent yields. Benzyl ethers such as isochroman and phthalan were converted
to 3,4-dihydroisocoumarin and phthalide in quantitative yields.
Oxidations are of fundamental importance to synthetic
organic chemistry, and numerous methods are reported in
the literature.1,2 The laboratory-scale liquid-phase benzylic
oxidations are generally carried out with a large excess of
metal oxidants such as chromium reagents and manganese
reagents.2 Since the metal residues are environmentally
undesirable and often provide problems during reaction and
workup, development of oxidizing methods requiring only
a catalytic amount of metal reagent in combination with
appropriate stoichiometric oxidant is a subject of interest.
There are reports on the catalytic methods for benzylic
oxidation including CrO3/t-BuOOH,3 heterogeneous chro-
mium catalysts/t-BuOOH,4 Cr(CO)6/t-BuOOH,5 heteropoly-
oxometalate/O2,6 N-hydroxyphthalimide/O2,7 CoCl2/O2,8 co-
balt Schiff base complexes/O2,9 Mn(salen)/NaOCl,10 RuCl3/
NaOCl,11 RuCl2(PPh3)3/t-BuOOH,12 Ni(bpy)2Cl2/NaOCl,13
and CeO2/NaBrO3.14 However, these methods have disad-
vantages and limitations, and new oxidation methods are still
desired.
Recently the Merck group reported a novel CrO3-catalyzed
oxidation of primary and secondary alcohols to carboxylic
acids and ketones with H5IO6 as the terminal oxidant.15 We
(6) (a) Nakayama, K.; Hamamoto, M.; Nishiyama, Y.; Ishii, Y. Chem.
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(c) Matsunaka, K.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. Tetrahedron Lett.
1999, 40, 2165. (d) Einhorn, C.; Einhorn, J.; Marcadal, C.; Pierre, J.-L.
Chem. Commun. 1997, 447.
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Compounds; Academic Press: New York, 1981.
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D.; Dakka, J.; Neeleman, E. Stud. Surf. Sci. Catal. 1994, 83, 407. (c) Cr-
MCM-41: Das, T. K.; Chaudhari, K.; Nandanan, E.; Chandwadkar, A. J.;
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10.1021/ol991175k CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/03/1999