Stereoselective synthesis of novel monocyclic trans-3-halogenated-4-pyrazolyl-β-lactams: Potential synthons and promising biologically active agents
Stereoselective synthesis of novel monocyclic trans-3-halogenated-4-pyrazolyl-β-lactams 5 is described. The reaction of ketene derived from α-bromo/chloroethanoic acids 4 using POCl3 and Et3N with pyrazolyl substituted imines 3a–d in refluxing toluene resulted exclusive formation of trans-β-lactams through [2 + 2] through cycloaddition reaction. The chemical structures of all the newly synthesized β-lactams were verified on the basis of spectroscopic techniques such as FTIR, 1H NMR, 13C NMR, and elemental analysis (CHN). The trans configuration of β-lactams 5 was assigned with respect to position of C3-H and C4-H. The novel β-lactams 5 are potential synthons for azetidines, aziridines, 3-unsubstituted azetidinones, 3-alkyl-halo-azetidinones, and promising biologically active agents.