Dehydrohalogenation of threo- and erythro-1-chloro-and 1-bromo-1,2-diphenyl-2-p-tolylsulphonylethanes. A survey of the stereochemical course

Abstract

The stereochemical course of the dehydrohalogenation of the diastereoisomeric 1-chloro- and 1-bromo-1,2-diphenyl-2-p-tolylsulphonylethanes (I)–(IV) has been studied. A broad spectrum of base–solvent pairs has been employed. For all the reagents used the erythro-isomers (I) and (III) invariably gave anti-elimination. The threo-isomers (II) and (IV) followed a course strongly dependent upon the nature of the base. In reactions promoted by anionic bases the importance of the syn-component increased with the strength of the reagents. Addition of a crown ether did not cause a significant effect. When amines were used the stereochemical outcome was influenced by the nature of the leaving group, of the solvent, and of the attacking base. The observations are briefly discussed in the light of current views concerning elimination reactions. The use of diethylaminomethylpolystyrene as a dehydrohalogenating agent has been also tested.