Transformations of penicillins and cephalosporins: reactions of chlorosulphonyl isocyanate with penams, cephems, and azetidin-2-ones

Abstract

Benzyl 6β-phthalimidopenicillanate reacted with chlorosulphonyl isocyanate to give a thiazolo[3,2-c]pyrimidine derivatives by ring expansion of the β-lactam. The trimethylsilyl derivative of 2,2,2-trichloroethyl 6β-phenoxyacetamidopenicillanate gave two isomeric thiazolo[3.2-c]pyrimidine derivatives. Methyl 3-methyl-7β-phenoxyacetamidoceph-3-em carboxylate gave a pyrimido[6,1-b][1,3]thiazine derivative. (3R,4R)-3-Phthalimido-1-(1-benzyloxycarbonyl-2-methylprop-1-enyl)-4-methylthioazetidin-2-one did not give a corresponding β-lactam ring expansion product, but gave epimeric 4-chloro-products by replacement of the 4-methylthio-group. 4-Acetoxyazetidin-2-one reacted with chlorosulphonyl isocyanate to give an N-allophanoyl derivative.