C. Boga et al., A new synthesis of chloroheterocycles via metal-halogen exchange between trichloroacetyl derivatives and heteroaromatic lithium and Grignard reagents, J ORGMET CH, 588(2), 1999, pp. 155-159
The reaction between 2-lithio derivatives of aromatic azaheterocycles and t
richlorocetyl derivatives rapidly produces the corresponding 2-chloro deriv
atives in high yields through a metal-halogen exchange mechanism. The use o
f ethyl trichloroacetate can give better results with respect to those obta
ined with trichloroacetyl chloride, which probably involves dichloroketene
formation. The reaction with Grignard reagents is more complex: in fact, 2-
benzothiazolylmagnesium chloride with ethyl trichloroacetate or trichloroac
etyl chloride gives 2-chlorobenzothiazole together with considerable amount
s of ethyl 1,3-benzothiazole-2-carboxylate or 2-benzothiazolyl dichlorometh
yl ketone, respectively. (C) 1999 Elsevier Science S.A. All rights reserved
.