Selective Formation of 1,3,4-Trisubstituted and 3,4-Disubstituted Trans-β-lactams from Zinc Enolates and Imines

Article abstract of DOI:10.1002/recl.19871060910

A new route for the high yield synthesis (better then 90 percent) of exclusively trans-β-lactams (azetidin-2-ones) is reported which involves the 1:1 reaction of an α-aminoacid ester zinc enolate with an appropriate imine.The reaction can be carried out as a 'one-pot' synthesis as has been demonstrated for the synthesis of trans-3-diethylamino-4-phenyl azetidin-2-one (93 percent yield).The novel zinc enolates have most likely a Z-geometry as a result of intramolecular chelate coordination.Evidence has been obtained that in the first step these zinc enolates react with the imine in a highly diastereoselective manner providing the threo aldolate which in a subsequent step undergoes ring closure to the azetidin-2-one.