Reaction of 2-(trifluoromethyl)chromones with pyridoxal: Formation of 1-benzopyranooxepino- and 1-benzopyranopyranopyridines

Pyridoxal undergoes oxa-Michael initiated ring closure with 2-(trifluoromethyl)chromones giving 11a,13-dihydro-6H-1-benzopyrano[3′,2′:6,7]oxepino[3,4-c]pyridin-6-ones and 6H,11aH-1-benzopyrano[3′,2′:5,6]pyrano[2,3-c]pyridin-6-ones. Participation of alcoholic hydroxy group of pyridoxal in the initial oxa-Michael addition leads to the former product and that of the phenyl hydroxy group to the later one.