Intramolecular 1,3-dipolar cycloaddition at the periphery of heterocyclic systems. Part 1. Facile oxime–nitrone isomerisation at the periphery of pyran and 1-benzopyran

Abstract
4-(Alk-2-enylamino)-2-oxo-2H-1-benzopyran-3-carbaldehyde oximes 5 underwent thermally induced 1,3-dipolar cycloaddition under mild conditions giving isoxazolo[3,4-d][1]benzopyrano[4,3-b]pyridine derivatives 6 in good yields. The features of the oxime–nitrone isomerisation and nitrone–olefin cycloaddition are discussed.