Transformations of Penicillins.: Part IV. On the Trapping of Sulphenic Acids from Penicillins with Thiols

On heating, penicillin S-oxides form equilibrium mixtures with the corresponding sulphenic acids. The sulphenic acids can be trapped intermolecularly with a variety of reagents, including thiols. The disulphides (3) so obtained react with trialkyl phosphites to produce the corresponding sulphides, the alkyl residue arising from the phosphite reagent. Cleavage of the nitrogen-containing substituent from the disulphides or sulphides was effected by addition of diazomethane across the double bond of the unsaturated ester to give an epimeric mixture of pyrazolines, which was then treated with base or reduced. The pyrazolines could also be reduced with NN′-dihydrobenzo[c]-cinnoline, a new, mild reducing agent.