A novel and facile stereocontrolled synthetic method for polyhydro-quinolines and pyridopyridazines via a diene-transmissive Diels–Alder reaction involving inverse electron-demand hetero Diels–Alder cycloaddition of cross-conjugated azatrienes

Cross-conjugated azatrienes bearing an electron-withdrawing sulfonyl or benzoyl group on the nitrogen atom underwent, on heating or in the presence of a Lewis acid (TMSOTf), an initial inverse electron-demand hetero Diels–Alder reaction with electron-rich dienophiles (vinyl ether, vinyl thioether, and allenyl ether) to produce 1:1 cycloadducts with high endo selectivity. The initial cycloadducts thus obtained underwent a second Diels–Alder reaction stereoselectively on the newly formed diene unit with electron-deficient dienophiles to give the crossed bis-cycloadducts, octahydroquinolines, with high diastereo-π-facial selectivity. The N-sulfonylazatrienes tethering an ortho-cinnamyloxyphenyl dienophile at the triene terminal underwent an initial intramolecular hetero Diels–Alder reaction of the inverse electron-demand type. The subsequent second Diels–Alder reaction of the formed mono-cycloadducts completed the diene-transmissive hetero Diels–Alder protocol to give benzopyrano[3,4-c]quinolines in a highly stereoselective manner.