Benzopyrones. Part IV. Pyrano[1,4]benzoxazinones and some dihydrobenzoxazines: synthesis, mass, and nuclear magnetic resonance spectra

Abstract

Nitrochromones with an aliphatic carbonyl-containing substituent have been selectively reduced to the amines, which cyclise spontaneously to the dihydropyrano[2,3-f]- and dihydropyrano[3,2-f]-[1,4]benzoxazines (10) and (12). The t-butyl ketone (5) on similar treatment gave the pyrano[2,3-f][1,4]benzoxazine (13) only. The conformation of the dihydro-oxazine ring of several compounds has been studied by n.m.r. spectroscopy; vicinal coupling constants are deduced. The mass spectra of several 3,4-dihydro-1,4-benzoxazines, some of which contain a fused pyrone ring, are reported and interpreted.