STUDIES ON THE REGIOSELECTIVITY OF INTERMOLECULAR DIELS-ALDER CYCLOADDITIONS OF 1-METHYLPYRANO[3,4-B]INDOL-3-ONE AND THE N-ACETYLATED DERIVATIVE

Diels-Alder reactions of the 1-methylpyrano[3,4-b]indol-3-one 1a with less than two equivalents of methyl acrylate and methyl vinyl ketone occur with complete regioselectivity to yield the corresponding 3-substituted 1-methyl-1,2-dihydrocarbazole derivatives 3.Cycloadditions of the N-acetyl-1-methylpyrano[3,4-b]indol-3-one 1b with the same dienophiles proceed at a much slower rate to yield adducts incorporating two molecules of the dienophile. In this case the regioselectivity appears to have been reversed in both steps of the Diels-Alder reaction since the bis-adducts obtained as major products have the substituents on the C2 and C2' carbon. The reaction of 1a with the symmetrical dienophile dimethylfumarate produces a mixture of the cis and trans 1-methyl-9H-1,2-dihydrocarbazole-2, 3-dicarboxylic acid dimethyl esters 16 and 17 in the ratio of 1 : 3.7 respectively. © 1990.