Novel Syntheses of Azetidines and Azetidinones

A review of methods of preparation of azetidines and azetidinones, with emphasis on stereoselective routes. For the preparation of azetidines, a variety of syntheses involving nucleophilic substitution are discussed, as well as ring rearrangements, reduction of azetidin-2-ones, and other heterocyclizations. The Staudinger reaction between imines and ketenes is a common method for the synthesis of azetidin-2-ones (β-lactams), and is discussed in detail. A variety of other heterocyclization routes to β-lactams are also presented.