Synthesis and properties of 3-oxo-1,2-diazetidinium ylides

Article abstract of DOI:10.1021/ja00416a009

Treatment of α-chloroacylhydrazones of diaryl and certain aralkyl and dialkyl ketones with sodium hydride in anhydrous tetrahydrofuran gives 1-(disubstituted methylene)-3-oxo-1,2-diazetidinium inner salts (ylides). The reaction pathway involves formation of the hydrazone anion followed by intramolecular S_N2 halide displacement (with complete inversion at the α carbon) by the sp² imine nitrogen. These 1-(disubstituted methylene)-3-oxo-1,2-diazetidinium ylides are reduced by sodium borohydride to give 1-substituted 1,2-diazetidin-3-ones, undergo dipolar cycloaddition reactions to give fused aza-β-lactams, and can be hydrolyzed with p-toluenesulfonic acid monohydrate to the p-toluenesulfonic acid salt of 1,2-diazetidinone.