Abstract
The hetero Diels-Alder reaction of 4, 7-indoloquinones with crotonaldehyde dimethylhydrazone afforded 5-methyl-5, 6-dihydropyrido[6, 5-b]indole-4, 9-dione ([1, 8] isomer) and 5-methyl-5, 6-dihydropyrido[5, 6-b]indole-4, 9-diones ([1, 5] isomer). The 6, 7, 8, 9-tetrahydrocarbazole-2, 5-dione region-selectively afforded 4-methyl-1, 4, 6, 7, 8, 9-hexahydropyrido[2, 3-b]carbazole-5, 11-dione. The regiochemistry of these reactions was controlled by the substitution of the nitrogen and the 2-C atom of the indole moiety : the unsubstituted quinones afforded the [1, 8] regioisomer, whereas the [1, 5] compounds were obtained with the quinones bearing an electron-withdrawing substituent on the nitrogen or the 2-C atom.
