BENZOPYRANS .33. [4-DIMETHYLHYDRAZONES AND ANILS OF 2-UNSUBSTITUTED AND 2-METHYL-4-AXO-4H-1-BENZOPYRAN-3-CARBOXALDEHYDE WITH N-PHENYLMALEIMIDE(2]CYCLOADDITION OF N,N)
Ck. Ghosh et al., BENZOPYRANS .33. [4-DIMETHYLHYDRAZONES AND ANILS OF 2-UNSUBSTITUTED AND 2-METHYL-4-AXO-4H-1-BENZOPYRAN-3-CARBOXALDEHYDE WITH N-PHENYLMALEIMIDE(2]CYCLOADDITION OF N,N), Tetrahedron, 50(16), 1994, pp. 4905-4912
The chromone derivatives 1, 2, and 4 give with N-phenylmaleimide the c
ycloadducts 5, 12, and 13 which are converted by palladised charcoal i
nto 2-azaxanthone 6, xanthones 14 and 15, respectively. Treatment of t
he azaxanthone 5 with acidic ethanol produces a mixture of salicyloyl-
pyridines 7-9.