Regioselectivity and control in alkene formation from a carbonium ion after diphenylphosphinoyl migration

Abstract

Conversion of 2-hydroxyalkyldiphenylphosphine oxides into allylphosphine oxides by acid-catalysed diphenyl-phosphinoyl migration shows complete regioselectivity in favour of the more substituted olefin when the migration origin is unsymmetrical. The other, less substituted olefin is formed exclusively when a trimethylsilyl group is present on the appropriate carbon atom as it both increases the rate of the rearrangement and is lost in preference to a proton. The allylphosphine oxides are used in diene synthesis.