Stereoselective synthesis of chiral 4-(1-chloroalkyl)-β-lactams starting from amino acids and their transformation into functionalized chiral azetidines and pyrrolidines

Chiral short-chain alpha-chloroaldehydes were prepared starting from enantiomerically pure amino acids in a three-step approach, thus providing a practical synthetic alternative for known organo-catalytic alpha-chlorination procedures. The latter aldehydes proved to be useful starting materials for the stereoselective Staudinger synthesis of (3S,4S)-4-[(1S)-1-chloroalkyl]azetidin-2-ones in high diastereomeric ratios and good overall yields, which were used as chiral building blocks for the preparation of a number of azetidines and pyrrolidines