Phosphorus in organic synthesis. XII. Amino acids and peptides. XXII. Reaction of penicillin sulfoxides with diethyl phosphorocyanidate (DEPC).

Abstract
Reaction of penicillin sulfoxides with diethyl phosphorocyanidate (DEPC) was investigated. Treatment of a benzylpenicillin (S)-sulfoxide methyl ester with a slight excess of DEPC in N,N-dimethylacetamide gave a 3-cephem, a 2-cephem and a 3-methylenecepham in 22, 4 and 4% yields, respectively. Increase of the quantity of DEPC to a 3- or 5-fold excess increased the yield of the 3-cephem. Phenoxymethylpenicillin (S)-sulfoxide methyl ester also afforded a 3-cephem and a 3-methylenecepham under analogous reaction conditions as above, while phthalimidopenicillin (R)-sulfoxide methyl ester furnished a 3-cephem and 2 isothiazolones.

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