Di-t-butyl Chromate-Pyridine

[1189-85-1]  · C8H18CrO4  · Di-t-butyl Chromate-Pyridine  · (MW 230.22)

[110-86-1]  · C5H5N  · Di-t-butyl Chromate-Pyridine  · (MW 79.10)

(reagent for oxidizing alcohols and silyl ethers to aldehydes and ketones)

Alternate Name: t-butyl chromate-pyridine; chromyl chloride-pyridine-t-butanol.

Preparative Methods: prepared in situ from chromyl chloride, pyridine, and t-butanol to afford the tripyridine (x = 3) complex1 or from chromium(VI) oxide, t-butanol, and pyridine to yield a complex which may contain 1 to 3 equivalents (x = 1-3) of pyridine.2

Handling, Storage, and Precautions: all chromium(VI) reagents must be handled with care; the mutagenicity of CrVI compounds is well documented.3 This reagent should be handled in a fume hood.

Oxidation of Alcohols to Carbonyl Compounds.

Addition of Chromyl Chloride to a solution of pyridine in dichloromethane, cooled in a dry ice-acetone bath, gave a strong oxidizing mixture which oxidized primary alcohols to aldehydes in good to excellent yields on a small scale.1 Addition of t-butanol generated a milder oxidant which could be Di-t-butyl Chromate or a di-t-butyl chromate-tripyridine complex.1,4,5 This reagent is suitable for both small and large scale reactions. Cinnamyl alcohol, cyclododecanol, citronellol (eq 1), 1-dodecanol, and geraniol (eq 2) are oxidized to the corresponding carbonyl compounds in 86, 97, 93, 99, and 100% yield, respectively.1 Although this reagent is inferior to the Collins reagent (see Dipyridine Chromium(VI) Oxide) for oxidizing allylic alcohols owing to isomerization of the carbon-carbon double bond (eq 2), it offers advantages for the oxidation of simple saturated primary alcohols.

The reagent prepared from chromium(VI) oxide oxidizes primary trimethylsiloxy groups to aldehydes and does not attack acid-labile groups, double bonds, ether groups, or allylic methylene groups in the same molecule.3 Although secondary silyl ether groups are oxidized to ketones by the reagent, they are stable to the experimental conditions used for the oxidation of primary silyl ether groups. For example, (±)-[(1R,2S,3R,5S)-2-[(trimethylsiloxy)methyl]-3-(trimethylsiloxy)-6-oxabicyclo[3.3.0]octan-7-one is oxidized to (±)-[(1R,2S,3R,5S)-2-formyl-3-(trimethylsiloxy)-6-oxabicyclo[3.3.0]octan-7-one.

It is of interest to note that di-t-butyl chromate oxidizes primary aliphatic alcohols in benzene or petroleum ether at room temperature to a mixture of the aldehyde, acid, and the ester of the acid.5 It oxidizes cinnamyl alcohol and geraniol to the corresponding aldehydes in 61 and 77% yield, respectively.5

1. Sharpless, K. B.; Akashi, K. JACS 1975, 97, 5927.
2. Palme, H. J.; Erhart, B.; Schwarz, S.; Weber, G.; Henkel, H.; Moellmann, P.; Nowak, H.; Pieper, A.; Dittmann, P.; et al. East Ger. Patent 298 238, 1992 (CA 1992, 117, 7232).
3. Cupo, D. Y.; Wetterhahn, K. E. Cancer Res. 1985, 45, 1146 and references cited therein.
4. Luzzio, F. A.; Moore, W. J. JOC 1993, 58, 512.
5. Suga, T.; Kihara, K.; Matsuura, T. BCJ 1965, 38, 893.

Fillmore Freeman

University of California, Irvine, CA, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.