Dicarboxylates of 3-Methylidene-β-lactams: Addition Reactions to the Exocyclic Double Bond, Formation of Spiro-β-lactams, and Reductive Ring Opening by Hydrazines

Synthetic Approaches toward Monocyclic 3-Amino-β-lactams

Due to the emerging resistance against classical β-lactam-based antibiotics, a growing number of bacterial infections has become harder to treat. This alarming tendency necessitates continued research on novel antibacterial agents. Many classes of β-lactam antibiotics are characterized by the presence of the 3-aminoazetidin-2-one core, which resembles the natural substrate of the target penicillin-binding proteins. In that respect, this Review summarizes the different synthetic pathways toward this key structure for the development of new antibacterial agents. The most extensively applied methods for 3-amino-β-lactam ring formation are discussed, in addition to a few less common strategies. Moreover, approaches to introduce the 3-amino substituent after ring formation are also covered.