Reaction of 3-chloro-1,2-benzisothiazole with diethyl malonate in the presence of tetra-alkylammonium salts. Properties and X-ray crystal structure analysis of 3-(3-aminobenzo[b]thiophen-2-yl)-1,2-benzisothiazole

Abstract

3-Chloro-1,2-benzisothiazole (I) reacts with diethyl malonate, in the presence of quaternary ammonium bases, under conditions of phase-transfer catalysis to give products such as, in the reaction with diethyl sodiomalonate, diethyl 1,2-benzisothiazol-3-ylmalonate (IV) and ethyl 1,2-benzisothiazol-3-ylacetate (V), formed by normal nucleophilic substitution at the 3-position, and diethyl (2-cyanophenylthio)malonate (II) and ethyl 3-aminobenzo[b]thiophen-2-carboxylate (III), produced by scission of the isothiazole ring. However, in one case the reaction, carried out according to Makosza, is more complex and mainly proceeds towards the 3-(3-aminobenzo[b]thiophen-2-yl)-1,2-benzisothiazole (VII), a product which was not previously identified and whose structure we have now established from chemical and spectral properties and X-ray crystal structure analysis. The structure of (VII) was determined from X-ray diffractometer data by direct methods and refined by least-squares to R 0.055 for 1 150 independent reflections.