Patent ID: 7358356

Claim:
A method for preparing a β-lactam compound, which comprises the following steps: reacting a compound of Formula (2), wherein A represents a condensed heterocyclic group having a β-lactam ring structure, and M represents a hydrogen atom or a metal atom, in a polar organic solvent, with a 4-halogenomethyldioxolenone compound of Formula (3), wherein R 1 and R 2 each independently represent a hydrogen atom, an optionally substituted C 1 -C 6 alkyl group or an optionally substituted phenyl group, or R 1 and R 2 together form an optionally substituted C 3 -C 8 ring, and X represents a halogen atom, to result in a reaction solution containing a β-lactam compound in the polar organic solvent; dehydrating a polar organic solvent solution obtained as the reaction solution or obtained by working up the reaction solution, to bring the concentration of water below a given level, wherein the dehydration step comprises distilling off water together with the polar organic solvent while adding a polar organic solvent to the solution, or comprises repeating two or more cycles of adding a polar organic solvent to the polar organic solvent solution and then distilling off water together with the polar organic solvent wherein the polar organic solvent further contains an iodine compound.