Studies related to penicillins. Part IV. The rearrangement of penicillanic acid derivatives to 1,4-thiazepines

Abstract

Methyl 6α-chloropenicillanate rearranges to methyl (3S)-6-chloro-2,3,4,7-tetrahydro-2,2-dimethyl-7-oxo-1,4-thiazepine-3-carboxylate when treated with antimony pentachloride in dichloromethane. Under similar conditions methyl penicillanate and methyl 6β-phthalimidopenicillanate undergo analogues isomerisations. The racemic α-isomer of 4-methoxycarbonyl-5,5-dimethyl-α-phthalimidothiazolidine-2-acetic acid is converted into methyl (3RS)-2,3,4,7-tetrahydro-2,2-dimethyl-7-oxo-6-phthalimido-1,4-thiazepine-3-carboxylate by treatment with phosphoryl chloride in benzene.