Study on Direct Benzoannelations of Pyrrole and Indole Systems by Domino Reactions with 4,5-Dicyanopyridazine

Abstract—The title pyridazine 1 was found to undergo hetero Diels–Alder [4þ2] cycloadditions on the C(2)–C(3) double bond of pyrrole and indole systems; spontaneous loss of nitrogen from the primary adducts, followed by oxidation processes, afforded the corresponding fully aromatic benzoannelated skeletons in modest and reasonable yields, respectively. Competitive attacks of the same systems at the strongly electrophilic C-4 carbon of 1, leading to substitution products, were evidenced.