Asymmetric synthesis of trans-3-amino-4-alkylazetidin-2-ones from chiral N,N-dialkylhydrazones.

Enantiopure N,N-dialkylhydrazones 3 smoothly react with N-benzyloxycarbonyl-N-benzyl glycine as an aminoketene precursor to afford trans-3-amino-4-alkylazetidin-2-ones 4 as single diasteromers. As an exception, hydrazone 3f (R = OBn) affords cis-(3R,4R)-4f under modified conditions. N-N Bond cleavage of cycloadducts 4 afforded free azetidinones 5 in high yields. [structure: see text]