CYCLIZATION REACTIONS OF 2,2'-BIS-N-METHYLINDOLYL TO POTENTIAL PROTEIN-KINASE-C INHIBITORS

2,2'-Bis-N-methylindolyl (4) was used as the starting material in the syntheses of some indolo[2,3-a]carbazoles (6, 7, and 10a,b). Compounds of this type represent the subunit of the staurosporine group of substances, a natural class of protein kinase C inhibitors. Reaction of the bisindolyl (4) with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate - in the sense of a Diels-Alder reaction with inverse electron demand - gave rise to the pyridazino[b]indoles (11b, 11b') as an isolable mixture of diastereomers and additionally to a rearranged product (13).