Design of hybrid heterocyclic systems with a furoxanylpyridine core via tandem hetero-Diels–Alder/retro-Diels–Alder reactions of (1,2,4-triazin-3-yl)furoxans

Abstract

Two convenient, facile, regioselective and highly effective one-pot protocols for the synthesis of previously unknown hybrid heterocyclic systems with the furoxanylpyridine core based on the tandem inverse-electron-demand hetero-Diels–Alder/retro-Diels–Alder reactions of the tailor-made (1,2,4-triazin-3-yl)furoxans with 1-(pyrrolidino)cyclohexene and norbornadiene have been developed. The methods comprise [4 + 2] cycloaddition of enamine or norbornadiene to the 1,2,4-triazine ring of (1,2,4-triazin-3-yl)furoxans followed by one-pot transformation of the formed intermediates and this affords an extensive series of polyheterocyclic ensembles combining furoxan and pyridine (tetrahydroisoquinoline, indenopyridine, terpyridine) rings in one molecule through a C–C bond in good to excellent yields.