Cyclisation of Schiff bases containing amide or hydroxamic acid groups to 1,2-dihydroquinazolin-4-ones; thermal decomposition reactions of the 1,2-dihydroquinazolin-4-ones

Abstract

2-Hydroxynaphthalene-1-carbaldehyde reacts with o-aminobenzamide in methanol to produce the Schiff base (1a) whereas reaction with 2-aminobenzohydroxamic acid leads directly to the dihydrohydroxyquinazolinone (2b). The Schiff base (1b), an intermediate in the formation of (2b), can be isolated (in an impure form) by quenching the reaction with water. When refluxed in dichlorobenzene the dihydrohydroxyquinazolinone (2b) decomposes in part by carbon-carbon bond fission to give 3-hydroxyquinazolin-4(3H)-one (5) and 2-naphthol and to a lesser extent by dehydration leading to the quinazolinone (4). The dihydroquinazolinone (2a) is readily prepared by cyclisation of the Schiff base (1a) and decomposes thermally to give quinazolin-4(3H)-one (9) and 2-naphthol. A mechanism for the carbon-carbon bond cleavage observed in the thermal decompositions is proposed.