Cyclic quaternary ammonium salts. Part VII. The deoxygenation of pyrido[1,2-a]pyrazinium 2-oxide salts

Abstract

The relative ease of deoxygenation of 1-substituted, 3-substituted, and 1,3-disubstituted pyrido[1,2-a]pyrazinium 2-oxide salts has been investigated; large hydrocarbon substituents in the 1- or 3-position facilitate-deoxygenation. Attempts to prepare 1,3-diphenylpyrido[1,2-a]pyrazinium 2-oxide salts from the quaternary salt formed between 2-benzoylpyridine oxime and phenacyl bromide gave, depending upon the reaction conditions, either the rearrangement product, 4-bromo-1,2-dihydro-1-oxo-2,3-diphenylpyrido[1,2-a]pyrazinium bromide, or 1,3-diphenylpyrido[1,2-a]pyrazinium bromide, the product of cyclisation accompanied by deoxygenation.