Electrocatalytic Annulation–Iodosulfonylation of Indole‐Tethered 1,6‐Enynes to Access Pyrrolo[1,2‐a]indoles

Abstract

We present the first example of electrocatalytic three‐component annulation–iodosulfonylation of indole‐tethered 1,6‐enynes with arylsulfonyl hydrazides and KI for accessing various iodosulfonated pyrrolo[1,2‐a]indoles in moderate to excellent yields with high stereospecificity. This electrosynthesis opens new avenues for the construction of pyrrolo[1,2‐a]indoles skeleton with good functional group compatibility under environmentally benign condition. Based on the control experiments and cyclic voltammetry data, we suggested the plausible reaction mechanism which included anodic oxidation, homolysis of arylsulfonyl iodide, arylsulfonyl radical addition, 5‐exo‐dig cyclization, radical coupling or nucleophilic attack of iodide ions cascade.

Photocatalytic Thio/Selenosulfonylation–Bicyclization of Indole-Tethered 1,6-Enynes Leading to Substituted Benzo[c]pyrrolo[1,2,3-lm]carbazoles

“…In light of the above findings and previous reports, ,,, Scheme illustrates a hypothetical mechanism for this photocatalytic bicyclization–thiosulfonylation process. First, when exposed to blue LEDs, fac -Ir­(ppy) 3 reached the excited state fac -Ir­(ppy) 3 *, which then interacted with 2a , leading to the formation of excited 2a * and the regeneration of fac -Ir­(ppy) 3 though an energy transfer (EnT) process.…”

“…For example, Zeng and co-workers accomplished a photocatalytic annulation–thiosulfonylation of silicon-based 1,7-enynes with thiosulfonates for forming a plethora of thiosulfonylated benzosilacycles in excellent yields (Scheme a). Encouraged by this impressive advance, and in conjunction with our continuing interest in radical transformations and bifunctionalization of indole-tethered 1,6-enynes, we believed that, when sila-enynes are replaced by indole-linked 1,6-enynes 1 as radical acceptors, the transformation can be directed toward visible-light-promoted annulation–bifunctionalization to form fused N -heteropolycyclic compounds 7 . Unexpectedly, the reaction proceeded along the direction of photocatalytic bicyclization–bifunctionalization to produce benzo­[ c ]­pyrrolo­[1,2,3- lm ]­carbazoles instead of the targets.…”

Accessing pyrrolo[1,2-a]indole derivatives via visible-light-induced dearomatizative cyclization of indoles

“…3 Consequently, numerous synthetic methods for the pyrrolo[1,2- a ]indole derivatives have been disclosed in the past few decades. 4 However, the method development of novel annulation patterns to especially access this motif with accurate three-dimensional (3D) disposition is still highly desirable for drug discovery. 5…”