Benzopyrans. Part 23. Nitrogen heterocycles fused with or linked to 1-benzopyran from 3-acyl-2-methyl-1-benzopyran-4-one

Abstract

The enamine (2), prepared from the title benzopyranone (1; R²= H, Me, and Ph) and dimethylformamide dimethyl acetal, on treatment with ammonia and hydroxylamine gives the fused pyridine (5) and pyridine 2-oxide (10), respectively. Hydrazine, phenylhydrazine, and guanidine undergo initial 1,6-addition to the enamine (2) ultimately giving the pyrazoles (14) and (15), and the pyrimidine (17), respectively. The pyridinioacetamidate (11), prepared from the enamine (2; R²= Me and Ph) and acetohydrazide, thermolyses to the fused pyridine (5). A refluxing ethanolic solution of the enamine (2; R²= Me and Ph) with ethyl glycinate forms the ester (18) which on treatment with ethanolic sodium ethoxide produces the azepine (20).