Cycloaddition reactions of cephalosporin compounds. IX—¹H and ¹³C NMR stereochemical study of the 1,3‐dipolar cycloadditions of diazoalkanes to 2‐methylenecephem derivatives

Abstract

A series of known and novel 2-methylenecephem derivatives were prepared and their reactions with diazomethane, phenyldiazomethane and diphenyldiazomethane were studied. The initially formed 1-pyrazolino derivatives easily underwent spontaneous loss of nitrogen, leading to 2-spirocyclopropylcephems. The two reaction products, formed in a 3: 1 to 8: 1 ratio on addition of diphenyldiazomethane, were separated by column chromatography and distinguished by their 'H and 13C NMR spectra. The 'H NMR spectra did not exclude the possibility of 1-pyrazoline formation, but elemental analysis and 13C data corroborated the previous assumption that loss of nitrogen took place, even in those cases when it did not occur during the reaction.