Studies related to penicillins. Part 21. β-Elimination reactions of S,S-dioxides of penicillanic esters

Abstract

In the presence of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), methyl benzylpenicillinate 1,1-dioxide (3a) is converted into (2S,3R)-1-(1-methoxycarbonyl-2-methylprop-1-enyl)-4-oxo-3-phenylacetamidoazetidine-2-sulphinic acid (5a). Corresponding reactions are observed with the p-nitrobenzyl and 2-iodoethyl esters of benzylpenicillinic acid 1,1-dioxide (3b and c), with methyl phenoxymethylpenicillinate 1,1-dioxide (3d), with methyl benzyloxypenicillinate 1,1-dioxide (3i), with methyl 6β-phthalimidopenicillanate 1,1-dioxide (3h), with methyl 6α-chloropenicillanate 1,1-dioxide (4b), and with p-nitrobenzyl penicillanate 1,1-dioxide (4c). Unidentified non-β-lactam products are produced when methyl penicillinate 1,1-dioxide (3e), methyl methylpenicillinate 1,1-dioxide (3f), and benzyl 6β-triphenylmethylaminopenicillanate 1,1-dioxide (3g) are treated with DBN.

The sodium salt of compound (5a) reacts with methyl iodide to give methyl 3-methyl-2-[(2R,3S)-2-methylsulphonyl-4-oxo-3-phenylacetamidoazetidin-1-yl]but-2-enoate (6a). Similar reactions occur with the sodium salts of the sulphinic acids derived from the sulphones (3b), (3d), (4b), and (4c).