2 + 2] Cycloaddition reactions between ketenes, bearing known. In this way β-lactams with a widely varying substitution pattern at the C-3 and C-4 positions of the ring amino-, oxy-, or halo-groups, and imines are recognized as being amongst the most important and direct routes to β-are constructed stereoselectively. The diastereoselection of the cycloaddition process can be controlled with variable lactams. Alkyl-substituted ketenes also furnished the corresponding β-lactams upon reaction with activated imines success from chiral groups attached to either the ketene or the imine component, or alternatively to both. This method, (iminoesters). In general, ketenes are generated from the appropriate acid chloride and a tertiary amine. The major or in turn, has proved to be valuable for the synthesis of precursors of important β-lactam antibiotics, and new sole product of the cycloaddition is usually the cis-β-lactam, although a few exceptions showing trans selectivity are successful applications can be expected in the near future.
tive structural classes (Figure 1) the penams 1, cephems 2,