Oxidative fission of some α-substituted β-diketones by selenium dioxide

Abstract

3-Acetyl-1,2,3,4-tetrahydroisoquinoline-1,4-dione (Ia), the β-diketone tautomer of 3-acetyl-1,2-dihydro-4-hydroxyisoquinolin-1-one (I), was oxidised to 1,2,3,4-tetrahydroisoquinoline-1,3,4-trione (VI) and acetic acid by selenium dioxide (1 mol). The proposed mechanism involves 1,2,3,4-tetrahydro-5′-hydroxy-5′-methylisoquinoline-3-spiro-4′-(1,3,2-dioxaselenolan)-1,4-dione (VIII). This β-diketone fission may be general, but not always recognised because of further oxidation of the characteristic products. 1,2,3-Triphenylpropane-1,3-dione (XV), in which ready oxidation of fission products is precluded, gave benzil and benzoic acid as the only products.