Cis and trans-4-Oxoazetidine-2-Sulphonic Acid Derivatives; Preparation and X-Ray Structure Determination

Cis and ćrans-4-oxoazetidine-2-sulphonic acid derivatives were prepared starting from penicillanate sulphoxides (1) and (4). The methylsulphonates (5), (7), (8) and (9) were formed by oxidation of 4-oxoazetidine-2-sulphinates (2), (3), and (6). Generally, 4-oxoazetidine-2-sulphonates were labile entities and hydrolyzed under mild conditions into sulphonic acids. These were isolated as acids (12) and salts (10), (11) and (14). The conformational isomers of the sulphonate (9a) were detected by 'H NMR spectroscopy and confirmed by variable temperature experiments. X-Ray structure analyses of 9a were performed but there wasn’t any evidence for intramolecular hydrogen bonding.