Preparation of compounds in the new dipyrrolo[3,4‐ b :3′,4′‐ e ]‐pyridine series from 1‐benzylidene‐2,3‐dioxopyrrolidines. A variation of the hantzsch synthesis

Treatment of easily prepared l‐substituted‐4‐benzylidene‐2,3‐dioxopyrrolidines with ammonium formate produces 1,2,4,6,7,8‐hexahydro‐2,6‐disubstituted‐8‐aryldipyrrolo [3,4‐ b :3′,4′‐ e ]pyridine‐3,5‐diones (II), usually in yields of 50 to 60%. Aromatization of the dihydropyridine ring of the hexahydroderivatives II yields corresponding 1,2,6,7‐tetrahydro‐2,6‐disubstituted‐8‐aryldipyrrolo[3,4‐ b :3′,4′‐ e ]pyridine‐3,5‐diones (III). These compounds appear to be the first to incorporate the dipyrrolo[3,4‐ b :3′,4′‐ e ]pyridine ring system.