Unusual stereoselection in the reaction of dianions derived from 1-phenylsulphonylalkan-2-ols with electrophilic reagents

Abstract

The stereochemistry in the reaction of dianions of 1-phenylsulphonylalkan-2-ols (1) with electrophilic reagents such as alkyl halides and aldehydes is discussed. The reaction takes place regioselectively at the α-position to the sulphonyl group to form a new chiral centre. In tetrahydrofuran the sterically more crowded erythro-isomer is obtained as the major product in a good diastereoisomeric ratio (50–100% d.e.). Additives such as HMPA and bulky diamines greatly influence the stereoselectivity of the reaction. The co-ordination of tetrahydrofuran molecules with a metal cation is considered to play an important role in the reaction.