Diastereoselective Michael addition of (S)-mandelic acid enolate to nitroalkenes. Enantioselective synthesis of α-hydroxy-α,β-diaryl-γ-lactams

The reaction of the lithium enolate of the (S,S)-cis-1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with several aromatic nitroalkenes in the presence of HMPA proceeds readily to give the corresponding Michael adducts in good yields and diastereoselectivities. Reduction of the nitro group with Zn/HCl/EtOH/H2O with concomitant intramolecular aminolysis of the acetal moiety leads directly to enantiomerically pure α-hydroxy-α,β-diaryl-γ-lactams.