Formation of spirocyclic indenopyrazine–pyridooxazines via 1,4-dipolar cycloaddition reaction

Abstract

The Huisgen’s 1,4-dipoles, generated from pyridines and dialkyl acetylenedicarboxylates, undergo dipolar cycloaddition reaction with the C=O bond of 9-oxo-9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile to afford dialkyl 2,3-dicyano-9a′H-spiro[indeno[1,2-b]pyrazine-9,2′-pyrido[2,1-b][1,3]oxazine]-3′,4′-dicarboxylates. When isoquinoline was used instead of pyridine, dialkyl 2,3-dicyano-11b′H-spiro[indeno[1,2-b]pyrazine-9,2′-[1,3]oxazino[2,3-a]isoquinoline]-3′,4′-dicarboxylates were obtained. The structure of a typical product was confirmed by X-ray crystallography. The good yields of the products, diastereoselectivity, and lack of activators or metal promoters are the main advantages of this method.