A new type of dimroth rearrangement: formation of 1,2-dihydro-3H-quinazolone 4-oximes from 4-amino-1,2-dihydroquinazoline 3-oxides

Abstract

Contrary to earlier claims the primary product of the reaction of aldehydes and o-aminobenzamide oxime is, irrespective of the aldehyde, always a 4-amino-1,2-dihydroquinazoline 3-oxide. Thermolysis of 1-unsubstituted 2-substituted quinazoline 3-oxides (5) in solution or in melt gives rise, by a new type of Dimroth rearrangement, to the isomeric 1,2-dihydro-4-quinazolone oximes (6), while the 1-benzyl 2-unsubstituted analogue (9j) yields, presumably by an addition–elimination ring transformation coupled with oxidation, a quinoidal quinazolone 4-oxime (17).