Stereodivergent synthesis of the enolates of a β-amino ester by using lithium N-benzyltrimethylsilylamide

Highly stereoselective generation of both Z- and E-enolates (1 and 3)² is accomplished by the conjugate addition of lithium N-benzyltrimethylsilylamide (LSA) to methyl crotonate. The alkylation with alkyl halides and aldol condensation with aldehydes via 1 and 3 are studied. The alkylation of 3 produces moderate to good syn selectivity, while that of 1 gives no selectivity. The aldol condensation of 1 affords the anti-syn isomer (11) predominantly, whereas that of 3 gives the syn-anti isomer (14) preferentially.