Stereo- and regio-control of electrophilic additions to cyclohexene systems by neighbouring groups: participation of allylic and homoallylic ester groups in hypobromous acid addition to some 5-unsaturated cholestane derivatives

Abstract

Hypobromous acid addition to 3β,7β-, 3δ,7α-, 3β,7β-, and 3α,7α-diacetoxycholest-5-ene (8)–(11) and 3β,7β,19- and 3β,7α,19-triacetoxycholest-5-ene (12) and (13) involves intramolecular participation of the neighbouring acetoxy group(s). Competing reaction pathways responsible for the product distribution are discussed. The relative importance of steric, electronic (Markownikoff), and stereoelectronic effects has been elucidated. The findings may be used for prediction of the reaction outcome. They also demonstrate that the purposeful introduction of a neighbouring group can direct the addition along the desired route.