Facile synthesis of novel α-methylene-pyrazole-carboxylate substituted imines and <italic>trans</italic>-β-lactams: Versatile synthons for diverse heterocyclic molecules.

A simple, facile, and high yielding stereoselective approach for the integration of α-methylene-pyrazole-carboxylates at the β-lactam nucleus is described. These monocyclic β-lactams have been synthesized by treatment of 2-phenoxy/benzylthio/phenylthio ethanoic acids or acetoxyacetyl chloride/phthalimidoacetyl chloride <bold>5a-e</bold> with novel α-methylene-pyrazole-carboxylate imines <bold>4a-c</bold> using Et3N and POCl3 in refluxing toluene. All of the newly synthesized α-methylene-pyrazole carboxylate imines <bold>4a-c</bold> and their β-lactam derivatives <bold>6a-h</bold> have been fully characterized by spectroscopic techniques such as FTIR, NMR (1H, 13C, and 13C DEPT-135), 2D-NMR (COSY and HSQC), and elemental analyses (CHN). The cycloaddition reaction was found to be highly stereoselective leading to the exclusive formation of <italic>trans</italic>-β-lactams <bold>6a-h</bold> and <italic>trans</italic> configuration was assigned with respect to coupling constant values of C3-H and C4-H. The novel β-lactams <bold>6a-h</bold> bearing α-methylene-pyrazole-carboxylate ring system will serve as useful synthons for highly functionalized acids, acetohydrazides/pyrazolones, alcohols, pyrazole carboxamides, peptides, and promising biologically active agents. [ABSTRACT FROM AUTHOR]