Tetrahedron Letters 41 (2000) 5423±5425
A bifunctional approach towards the mild oxidation
of organic halides: 2-dimethylamino-N,N-dimethylaniline
N-oxide
Sosale Chandrasekhar* and Malayalam Sridhar
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
Received 28 April 2000; accepted 23 May 2000
Abstract
The titled reagent incorporates an oxygen-centred nucleophile and a basic moietyÐin a suitably mutual
orientationÐin the same molecule. It oxidises various primary benzylic bromides to the corresponding
aromatic aldehydes under relatively mild conditions (MeCN/rt±50ꢀC/6±24 h) in high yields (83±97%), and
is thus a useful alternative to the Kornblum procedure. # 2000 Elsevier Science Ltd. All rights reserved.
The oxidation of organic halides to the corresponding aldehydes or ketones is a very useful
synthetic transformation which, in many cases, aords more convenient access to the carbonyl
compound than the oxidation of the corresponding alcohol.1,2 The earliest example of the oxi-
dation of an organic halide is apparently the Hass±Bender reaction involving a nitronate anion,
which was reported in 1949. (The older Sommelet reaction, employing hexamethylenetetramine,
is rather circuitous and less general.) Several new versions were reported in the ensuing decades,
most notably the Krohnke (pyridine/p-nitrosodimethylaniline) and the Kornblum (DMSO)
reactions. Amongst the simplest of the above procedures is apparently the Kornblum reaction, in
which the organic halide is re¯uxed in DMSO along with sodium bicarbonate; however, the high
temperature involved and the fact that only activated halides are reactive apparently limit its
scope. A relatedÐand attractiveÐmethod employs various amine N-oxides,1 3 but suers from
variable yields. Mechanistically, the above methods generally involve displacement of the halide
by an oxygen or nitrogen centred nucleophile, followed by a base-induced dehydro-elimination
via cleavage of a heteroatom±heteroatom bondÐthe actual oxidation step: e.g. 1 which represents
the Kornblum reaction (Scheme 1).
In the present study, it was envisaged that incorporating the heteroatom centred nucleophile
and the basic moiety in the same molecule would enhance reactivity, and thereby lead to a
methodology workable under relatively mild conditions. The system chosen was 2-dimethylamino-
N,N-dimethylaniline N-oxide 2, in which the mutual orientation of the N-oxide and the basic
* Corresponding author. Fax: +91 80 3600 529; e-mail: sosale@orgchem.iisc.ernet.in
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00874-1