Cycloaddition of 1,3-benzothiazole-2-sulfenyl(selanyl) chlorides to an activated acetylenic bond

Abstract

One of the current methods of synthesis of unsaturated heterocycles is the electrophilic cyclization of alkynes under the action of different electrophiles, including sulfenyl and selanyl chlorides, with ring closure via the nucleophilic participation of the heteroatom of the functional group in the starting unsaturated compound [1]. With the aim of developing another variant of cyclizations in the AdE reactions of unsaturated compounds (which includes ring closure with nucleophilic participation of a heteroatom found in the structure of the starting electrophile) we have studied the reaction of 1,3-benzothiazole-2-sulfenyl chloride (1a) or 1,3-benzothiazole-2-selanyl chloride (1b) with p-methoxyphenylacetylene (2). We have previously shown that the reactions of the hetarenechalcogenyl chlorides 1a,b with alkenes form the products of cycloaddition at the double bond, i.e. the 2H,3H-benzo[d][1,3]thi(selen)azolo[2,3-b][1,3]thiazol-4-ium salts [2-4]. At the same time, it has been shown that the reactions of hetarenesulfenyl chlorides (including compound 1a) with diphenylacetylene in methylene chloride gives only -chlorovinyl sulfides [5] as products of 1,2-addition. In the present work, we have used compound 2 as a model alkyne containing a p-methoxy substituent as a powerful electron donor in order to stimulate novel reaction routes.