REGIOSPECIFIC HETERO-DIELS-ALDER SYNTHESIS OF PYRIDO[2,3-B]CARBAZOLE-5,11-DIONES AND PYRIDO[3,2-B]CARBAZOLE-5,11-DIONES

Diels-Alder reactions of 2- or 3-bromocarbazolequinones (8) or (9) wit h azadienes (1) afford regiospecifically pyrido[2,3-b]- or pyrido[3,2- b]carbazole-5,11-diones (3) or (4). Structural assignment of the regio isomers is made by H-1-NMR NOE DIFF experiments. The orientation of th e cycloadditions is under control of the bromine atom position on quin ones (8) or (9). Calculations by the semiempirical method PM3 of the H OMO and LUMO orbital coefficients of azadienes (1) and quinones (2c), (8) and (9) indicate that the larger ones are situated at C-4 for azad ienes (1) and C-3 for the dienophiles.