Double stereodifferentiation in aldol reactions of pyroglutamic urethane esters

Abstract

Aldol condensation of the (2S)-pyroglutamate urethane ester 4 with (R)-glyceraldehyde acetonide 8 and with (S)-Garner aldehyde 14 gives excellent stereoselectivity at both of the chiral centres created in each of the reactions. The reactants therefore seem to be matched pairs, as the corresponding reactions with (S)-glyceraldehyde acetonide 10 and (R)-Garner aldehyde 16 are less stereoselective. Stereoselectivity was not so impressive in the aldol condensation between the bromide 20 and the aldehyde 8.