Lithium n-benzyltrimethylsilylamide (LSA): a new reagent for conjugate addition - enolate trapping reactions

Lithium N-benzyltrimethylsilyl amide (LSA) adds to crotonates in a 1,4-manner, though the reaction of ordinary lithium amides with α,β-unsaturated carbonyl compounds is accompanied with a 1,2-addition and hydrogen abstraction at the γ-position. The conjugate addition via LSA followed by enolate trapping with electrophiles produces the corresponding α-substituted β-amino esters, which are, in turn, converted into β-lactams and α-substituted α, β-unsaturated esters.