ELECTRON-TRANSFER-CATALYZED REACTIONS .7. AMINIUM SALT-INITIATED OXYGENATION OF KETENES - FORMATION OF SUCCINIC ANHYDRIDES

The aminium salt-initiated oxygenation of ketenes 1a and 1b with molec ular oxygen afforded in an unprecedented reaction mode the succinic an hydrides 2 and 3 within a few minutes at 0 degrees C. From mechanistic investigations it is inferred, that the regioselective 1,3-dipolar cy cloaddition of an intermediate a-lactone, independently trapped by cyc loaddition to hexafluoroacetone, to the ketene constitutes the final s tep of the reaction sequence. Surprisingly, the oxygenation reaction o ccurred even when the reaction was carried out with rigorous exclusion of atmospheric oxygen. Evidence is presented that aminium salts are c apable of both storing and activating molecular oxygen with remarkable efficiency, and that the reaction does not proceed via free ketene ca tion radicals.