AbstractReactions of indoline (I), 2‐methylindoline (II) and hexahydrocarbazole (III) with α,β‐unsaturated acids in the presence of polyphosphoric acid have been investigated. Reaction of 1 with acrylic acid afforded two compounds which were identified as 1,2,4,5‐tetrahydro‐6H‐pyrrolo‐[3,2,1‐ij] quinolin‐6‐one (IV) and 2,3,5,6,9,10‐hcxahydro‐1H‐cyclopenta[f lpyrrolo [3,2,1‐ij|‐quinoline‐1,8‐dione (VII). The reaction oi 1 with crotonic acid gave compounds V and VIII, analogous‐to IV and VII. The reaction of II with acrylic acid yielded two compounds VI and IX, whereas with crotonic acid, only X was isolated. With 111, acrylic acid afforded 5,6,8,9,10. 11,8a,11a‐octahydro‐4H‐pyrido[3,2,1‐jk]carbazol‐4‐one (XI) and a compound with a heretofore unknown ring system, viz., 2,3,5,6,7,8,11,12,5a,8a‐decahydro‐1H‐cyclopenta[h] pyrido [3,2,1‐jk |earbazole‐1,10‐dione. The structures of these compounds were deduced on the basis of their spectral and analytical data.