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

Benzyl 6ß-phthalimidopenicillanate reacted with chlorosulphonyl isocyanate to give a thiazolo[3,2-c]pyrimidine derivative by ring expansion of the ß-lactam. The trimethylsilyl derivative of 2,2,2-trichloroethyl 6ß-phenoxyacetamidopenicillanate gave two isomeric thiazolo[3,2-c] pyrimidine derivatives. Methyl 3-methyl-7ß-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 ß-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.