ASYMMETRIC-SYNTHESIS OF ALPHA'-SILYLATED ALPHA,BETA-EPOXY KETONES VIADARZENS REACTION

The diastereo- and enantioselective synthesis of alpha'-silylated alph a,beta-epoxy ketones via Darzens reaction is described. Using the SAMP /RAMP-hydrazone method alpha'-silylated alpha-bromo ketones (S)-4a and b were formed as enantiomerically pure starting materials for the Dar zens reaction with various aldehydes. The trans-epoxy ketones (S,SP)-6 a-g were obtained in good yields (55-80%) and with poor to good diaste reomeric excesses (de = 0-90%). Separation of diastereomers led to the enantiomerically pure title compounds (de,ee greater than or equal to 95%). In addition the Darzens reaction between the protected glyceral dehyde (R)-7 and alpha-bromopinacolone (8) afforded the cis-epoxy keto ne (R,R,R)-9 (de,ee greater than or equal to 95%).