Allenyl-β-lactams: versatile scaffolds for the synthesis of heterocycles.

The hybrid allenic β-lactam moiety represents an excellent building block for carbo- and heterocyclization reactions, affording a large number of cyclic structures containing different sized skeletons in a single step. This strategy has been studied under thermal and radical-induced conditions. More recently, the use of transition-metal catalysis has been introduced as an alternative that relies on the activation of the allenic component. On the other hand, the intramolecular version has attracted much attention as a strategy for the synthesis of bi- and tricyclic compounds in a regio- and stereoselective manner. This overview focuses on the most recently developed cyclizations on 2-azetidinone-tethered allenes along with remarkable early works accounting for the mechanism, as well as for the regio- and diastereoselectivities of the cyclizations.