Extended tandem reactions of 2H-1,2,3-triazole N-oxides with dialkyl acetylenedicarboxylates and N-phenylmaleimide: Substituted monocyclic 2,5-dihydro-1,2,3-triazines and new tetrahydrofuro[2,3-d]-1,2,3-triazoles. Azolium 1,3-dipoles. Part 5.

The reaction of substituted 1,2,3-triazole 1-oxides with dialkyl acetylenedicarboxylate dipolarophiles gave a new route to monocyclic 1,2,3-triazine derivatives via a multi-step sequence of cycloaddition, sigmatropic rearrangements, and ring expansion. With N-phenylmaleimide as dipolarophile, derivatives of a new tetrahydrofuro[2,3-d]-1,2,3-triazole system were formed. Mechanisms are discussed. An X-ray crystal structure of 2-(p-bromophenyl)-5-methoxalyl-5-methoxycarbonyl-4,6-dimethyl-2,5-dihydro-1,2, 3-triazine is reported.