Stereocontrol with phosphine oxides: synthesis of optically active cyclopropyl ketones
Treatment of β-keto γ′-hydroxy phosphine oxides, or silylated hemiacetal derivatives of these compounds, with potassium tert-butoxide in tert-butyl alcohol leads to the formation of cyclopropyl ketones. The synthesis of optically active 1,2-di- and 1,2,3-trisubstituted cyclopropyl ketones is described. The reaction is kinetically controlled and the ring-closure is generally stereospecific. A model is described to explain the stereochemical course of the reaction.