abstract |
Abstract 3-Exomethylenecepham sulfoxide esters are obtained in improved yields via cyclization of 3-methyl-2-(4-chlorosulfinyl-2-oxo-3-amino-1-azetidinyl)-3-butenoic acid esters under anhydrous conditions with a Lewis acid-type Friedel-Crafts catalyst in the presence of a nitro compound, e.g., nitromethane, nitroethane, nitropropane or nitrobenzene. |