An Update on the Synthesis of β-Lactams

Because the renewed interest of β-lactams in organic and medicinal chemistry, research in this field continues in producing new appealing progresses. This review tries to call the attention on synthetic aspects related to the generation of the four-membered heterocyclic ring, published in the last few years, with special accent in stereoselective synthetic approaches. The compendium will cover methods for achieving diastereo- and enantioselectivity during [2+2] cycloadditions, with the Staudinger reaction still as the first choice method, but also important achievements have been published for the imine-enolate condensation, the carbonylative cycloaddition, and the Kinugasa reaction. Significant success was also obtained in the synthesis of innovative 2-azetidinones through the formation of a single bond. In this respect, the C3-C4 bond formation, through intramolecular cyclization of linear epoxy or halo derivatives, and the carbenoid C-H insertion are among the most effectively exploited procedures. In addition, the adaptation of most procedures to solid-phase methodologies has facilitated the generation of molecular diversity based on the β-lactam skeleton.