A new synthesis of chloroheterocycles via metal-halogen exchange between trichloroacetyl derivatives and heteroaromatic lithium and Grignard reagents

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 .