Photochemical and thermal reactions of heterocycles. Part 5. Products via transient quasiantiaromatic azetine intermediates generated by desulphurisation of photochemical intermediates from a thiazolium-4-olate and 4-aminothiazolium salts

Abstract

Irradiation of the mesoionic triphenylthiazolium-4-olate (3) in the presence of tributylphosphine gave the quinolinone (7). This result was interpreted as arising via desulphurisation of the bicyclic intermediate (4) to the azetone (5), followed by its isomerisation to the ketene (6) and internal trapping. Similar irradiation of the 4-aminothiazolium salts (15) gave enamino nitriles (17) and benzoylacetonitrile (16). They are probably formed by isomerisation and hydration of the hitherto unknown quasiantiaromatic 2-imino-1,2-dihydroazete intermediates (20), which in turn are generated by desulphurisation of the bicyclic photochemical intermediates (19).