[4+2]-CYCLOADDITION AND [2+4]-CYCLOADDITION PROCESSES OF 4,5-DICYANOPYRIDAZINE WITH 2,3-DIMETHYLBUTA-1,3-DIENE

The title compounds afforded under relatively mild conditions the polycyclic systems 3a, 4, and 5 through alternative concomitant cycloadditions; the reactivity of the dicyanopyridazine system was critically influenced by the presence of methyl groups at the 3 and 6 positions. The skeleton of 3a and the stereochemistry of 5 were established by X-ray experiments.