Diastereoselective reactions of pyruvates with but-2-enyl organometallic compounds. Stereocontrol at the tertiary carbon centre

The reaction of pyruvates (3) with but-2-enyl-9-borabicyclo[3.3.1]nonane(2a) or its α-silyl and α-stannyl substituted derivatives (10) produced the threo-isomer [(4) or (11), respectively] stereoselectively; the latter reaction was applied to the synthesis of cis-crobarbatic acid(14).