Intramolecular 1,3-Dipolar Cycloadditions and Intramolecular Ene Reactions of 2-(Alkenyloxy)benzaldehyde Arylhydrazones

2-(3-Aryl-2-propenyloxy)benzaldehyde (or 1-naphthaldehyde) arylhydrazones undergo an intramolecular cycloaddition reaction via their 1,3-dipolar tautomers, azomethine imines, to the alkenyl group. Initial cycloadducts were converted to dehydrogenated compounds under the reaction conditions. On the other hand, introduction of cyano or ethoxycarbonyl groups instead of the aryl group into 3-position of the ortho propenyloxy group gave 3-cyanomethyl-4-chromanone arylhydrazones or the corresponding ethoxycarbonyl derivatives, respectively. The formation of these hydrazones was interpreted in terms of intramolecular ene reaction. The course of the reactions depends on the nature of the alkenyl substituents.