The N-arylimines of 2-(alk-2-enyl)amino-4-oxo-4H-pyrido[1,2-a]pyrimidine-3-carbaldehyde undergo the intramolecular [4+2] cycloaddition reaction under Lewis acid-catalyzed conditions to afford diastereomeric tetraazapentaphene derivatives. The diastereoselectivity as well as the scope and limitations of the cycloaddition reactions is discussed.
A Simple Oxime-Nitrone Isomerization and Intramolecular Nitronecycloaddition Reaction of 3-(Alk-2-enylamino)propionaldehyde Oximes.-The title oximes (V) undergo thermally induced 1,3-dipolar cycloaddition under mild conditions affording the isoxazolopyridines (VI). Appropriate substituents (e.g. methyl groups) at the 2-position in (V) restrict the conformational flexibility thus facilitating the cycloaddition. It is suggested that electron-withdrawing substituents on the hydroxyl amino group affect the oxime-nitrone isomerization step.-(NOGUCHI, MICHIHIKO; OKADA,
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