Asymmetric Synthesis of α′-Silylated α,β-Epoxy Ketones via Darzens Reaction
31 December 2000 (online)
The diastereo- and enantioselective synthesis of α′-silylated α,β-epoxy ketones via Diarzens reaction is described. Using the SAMP/RAMP-hydrazone method α′-silylated α-bromo ketones (S)-4 a and b were formed as enantiomerically pure starting materials for the Darzens reaction with various aldehydes. The trans-epoxy ketones (S,S,R)-6 a - g were obtained in good yields (55-80%) and with poor to good diastereomeric excesses (de = 0-90%). Separation of diastereomers led to the enantiomerically pure title compounds (de,ee ≥ 95%). In addition the Darzens reaction between the protected glyceraldehyde (R)-7 and α-bromopinacolone (8) afforded the cis-epoxy ketone (R,R,R)-9 (de,ee ≥ 95%).
asymmetric Synthesis - Darzens reaction - epoxy ketones - SAMP/RAMP-hydrazone method - α-silylated bromo ketones