Asymmetric synthesis of trans-disubstituted cyclopropanes using phosphine oxides and phosphine boranes.

The stereocontrolled synthesis of trans-disubstituted cyclopropylketones has been achieved from beta-alkyl, gamma-benzoyl phosphine oxides via a three-step cascade reaction incorporating an acyl transfer, phosphinoyl transfer and cyclisation to form the cyclopropane. Using Evans' chiral oxazolidinone auxiliary and by masking the phosphine oxide moiety as a phosphine borane we have extended the method to the synthesis of enantiomerically-enriched trans-disubstituted cyclopropyl ketones.