New entries into the indolizino[8,7-b]indole ring system

Tetrahydro-beta-carbolines 2 and 3 possessing a proton on nitrogen N-2 reac t with one molecule of activated alkyne to give, depending on the solvent, either enamines or heterocyclic derivatives of indolizino[8,7-b]indole skel eton. The enamines obtained can be quantitatively transformed into the same skeleton. The application of acidic or basic catalysis determines the posi tion of the double bond in the pyrrole ring as well as the nature of the su bstituents in positions 1,2,3 and 11b. (C) 1999 Elsevier Science Ltd. All r ights reserved.