Intramolecular condensation of steroidal α-acetoxy-ketones

Abstract

Intramolecular condensation of tertiary α-acetoxy-ketones in the cholestane series takes place in the presence of lithium di-isopropylamide to give products derived from nucleophilic attack of an ester enolate anion upon the adjacent oxo-group. When the acetoxy-group is axial, condensation proceeds rapidly at –78 °C to give the corresponding β-hydroxy-γ-lactone, but when it is equatorial the reaction is less efficient, and is attended by dehydration of the primary product.