Patent ID: 7273935

Claim:
A process for the preparation of 3-methylcepham-4-carboxylate of the formula (I) wherein R 2 and R 3 may be same or different and represent hydrogen, halogen, amino, alkyl, phenacetamido, substituted acetamido, phthalimido with a proviso that R 2 and R 3 are not both NH 2 , phenacetamido or phthalimido; R 1 represents a lower alkyl, p-methoxybenzyl, p-nitrobenzyl, o-nitrobenzyl, o-methoxybenzyl, o-chlorobenzyl or diphenylmethyl group, L represents a leaving group selected from the group consisting of chloro, bromo, iodo, tosylate, mesylate and triflate; which process comprises cyclizing the compound of formula (III) wherein Het represents a 5 or 6 membered—N— containing heterocyclic ring, which contains one or more heteroatoms selected from O, S and N, with a cyclizing agent, which introduces the leaving group L, in a polar organic solvent at a temperature in a range of −40° C. to 60° C., adding a solution of organic or inorganic nitrites, and isolating the compound of formula (I) without utilizing chromatographic techniques.