1,3-Dipolar cycloaddition reactions of vinylcephalosporins with diazoalkanes†

The vinylcephalosporin (1) undergoes a regio- and stereoselective 1,3-dipolar cycloaddition with diazomethane to give novel cephalosporins, a 3-pyrazolinocephem (4) and a double adduct (5). The vinylcephalosporin sulphoxide (2) gives only the pyrazolinocephem (7). In the reaction with diphenyldiazomethane upon heating the initially formed pyrazolines decompose and cyclopropylcephalosporin (9) formation takes place. The determination of the structures and stereochemistry of these compounds is also described.