TMEDA‐Catalyzed Regioselective Decarboalkoxy C−N Bond Formation: A Unified Direct Access to Indolo[2,1‐a]isoquinoline and Dibenzopyrrocoline Alkaloids

An unprecedented TMEDA‐catalyzed, regioselective, decarboethoxy direct C−N coupling protocol towards the synthesis of dibenzopyrrocolines 17 a–i and 5,6‐dihydroindolo[2,1‐a]isoquinoline 15 a–f/18 a–c alkaloids via the identification of N,N,N′,N′‐tetramethylethylenediamine (TMEDA) as a homogeneous catalyst is reported. The transition‐metal‐free, TMEDA‐catalytic novel protocol is operationally simple and showed a wide range of functional group tolerance and substrate compatibility. The gram‐scale application and synthesis of naturally occurring Cryptaustoline (dibenzopyrrocoline) alkaloid, further highlights the importance and versatile nature of the developed protocol. This finding also offers a TMEDA‐catalyzed direct synthesis of dibenzopyrrocolines and substituted 5,6‐dihydroindolo[2,1‐a]isoquinoline compounds in a one‐pot. The probable reaction pathway involves the free‐radical sequential approach via a single electron transfer (SET) mechanism. An unprecedented TMEDA‐catalyzed, regioselective, decarboethoxy direct C−N coupling protocol towards the synthesis of dibenzopyrrocolines 17 a–i and 5,6‐dihydroindolo[2,1‐a]isoquinoline 15 a–f/18 a–c alkaloids via the identification of N, N, N′, N′‐tetramethylethylenediamine (TMEDA) as a homogeneous catalyst is reported.