Enantioselective synthesis of 4-unsubstituted 3-alkoxy- and 3-aminoazetidin-2-ones from formaldehyde N,N-dialkylhydrazones

Playing two roles at once, chiral amines from L-proline or D-mannitol act as protecting groups and as chiral auxiliaries in the [2+2] cyclo-addition of formaldehyde hydrazones, such as 1, to ketenes. This strategy, based on the stability of the hydrazones as methanimines and on the development of a new oxidative cleavage of hydrazides, provides a short entry to enantiopure 4-unsubstituted 3-alkoxy- and 3-aminoazetidinones with desired configurations. X=OBn, N(CO<SUB2>Bn)Bn; Bn=benzyl; MMPP=magnesium monoperoxyphthalate.