Ring Expansions of β-Lactams and β-(thio)lactones

Abstract

The skeleton of β-lactams and β-lactones is present in biologically active compounds. For example, the β-lactam ring is present in classical antibiotics such as penicillins and cephalosporins. On the other hand, there are several natural products containing a β-lactone moiety, with interesting inhibitory activity. In addition, both fragments are very useful synthetic intermediates for the preparation of cyclic and acyclic compounds. The ring strain present in both motifs is involved in this versatile reactivity. This chapter is devoted to the synthesis of five-to sevenmembered heterocycles by ring expansion of β-lactams and β-lactones. Different methodologies have been described, and the mechanism for the formation of the products has been discussed. In addition, the applicability of some of the processes has been demonstrated by the synthesis of fragments of natural or biologically relevant compounds. The contributions presented in this chapter have been selected mainly from the developments achieved in the last decade.