Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 1651–1653
Pyridinium chlorochromate catalyzed oxidation of alcohols
to aldehydes and ketones with periodic acid
Mo Hunsen*
Department of Chemistry, Kenyon College, Tomsich Hall, Gambier, OH 43022, USA
Received 10 October 2004; revised 12 January 2005; accepted 17 January 2005
Available online 1 February 2005
Abstract—A facile pyridinium chlorochromate (PCC) catalyzed (2 mol%) oxidation of alcohols to ketones and aldehydes using
1
5 6
.05 equiv ofH IO in acetonitrile is described here.
Ó 2005 Elsevier Ltd. All rights reserved.
Oxidation, one the most fundamental reactions in syn-
thetic organic chemistry, has been the subject ofnumer-
Various alcohols were oxidized with PCC/H IO to give
5 6
the corresponding carbonyl compounds mostly in quan-
titative yields and the results are shown in Table 1. Most
1
,2
ous studies.
One ofthe reagents ofchoice ofr
oxidation ofprimary alcohols to aldehydes and second-
1
ofthe crude products were quite pure based on their
H
1
3
ary alcohols to ketones is pyridinium chlorochromate
3
and C NMR spectra. Benzylic 2° alcohols (entries 1, 3–
5) oxidize smoothly to give the ketones in a short
amount oftime. The aliphatic (entry 2) and homobenz-
ylic (entry 6) 2° alcohols also oxidized cleanly to the cor-
responding ketones with out any problems. It is worth
noting that the alkyne (entry 5) and cyclopropyl group
(entry 13) were not affected in this oxidation protocol.
(
PCC). Other methods include the Swern and co-work-
4
5
ers and Dess–Martin oxidations. Although PCC
oxidations are routinely performed in organic trans-
formations the requirement of at least a stoichiometric
amount ofPCC to complete the oxidation is a disadvant-
age due to the high toxicity ofchromium reagents (can-
cer suspect agents). Therefore, new methods for
oxidation ofalcohols to the corresponding carbonyl
compounds and that generate less chromium waste are
still needed.
6
An attempt to oxidize an allylic alcohol (cinnamyl alco-
hol) resulted in the of rmation ofa mixture ofproducts
(data not shown). Oxidation of1-naphthalenemethanol
(entry 7) gave the aldehyde without oxidation ofthe
7
naphthalene ring unlike the CrO /H IO oxidation.
3
5
6
We report herein a facile and efficient oxidation of pri-
mary and secondary alcohols to aldehydes and ketones.
Using only 2 mol% ofpyridinium chlorochromate
Benzyl alcohol (entry 8) as well as its electron poor
derivatives (entries 10 and 11) and electron-rich deriva-
tive (entry 9) all oxidized effortlessly to give correspond-
ing aldehydes in a very good to excellent yields. An
attempt to oxidize a benzylic diol (entry 12) gave the lac-
tone quantitatively and not a dialdehyde. Similarly our
attempt to oxidize a non-benzylic primary alcohol,
phenethyl alcohol (entry 14) delivered the ester cleanly
and not the aldehyde, while oxidation of1-octanol gave
a complex mixture.
(
PCC) and 1.05 equiv ofthe co-oxidant, H 5IO , in
6
acetonitrile we have oxidized 1° and 2° alcohols to the
corresponding carbonyl compounds (Scheme 1).
PCC (2 mol %)
H IO (1.05 equiv.)
OH
R'
O
5
6
R
R
R'
CH CN
3
We hypothesize that a covalently attached chloride ion
may facilitate the regeneration of the catalyst. No addi-
tion ofwater was required in contrast to the CrO /
Scheme 1.
3
7
H IO oxidation. We further hypothesize that the
5
6
Keywords: Oxidation; Alcohols; Catalysis; Pyridinium chlorochromate
PCC); Periodic acid; Aldehydes; Ketones.
PCC/periodic acid combination may form chlorochro-
matoperiodate (CCP), possibly a more powerful oxidiz-
ing agent than the chlorochromate (Scheme 2) and Cr
(
*
Tel.: +1 740 427 5091; fax: +1 740 427 5731; e-mail: hunsenm@
kenyon.edu
0
040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.01.076