Synthesis of indolo[2,1-a]isoquinoline derivatives via visible-light-induced radical cascade cyclization reactions

Abstract

We describe a photocatalyzed transformation for the synthesis of the indolo[2,1-a]isoquinoline core structure.

Electrochemical Tri‐ and Difluoromethylation‐Triggered Cyclization Accompanied by the Oxidative Cleavage of Indole Derivatives

“…For example, the challenging task of constructing functionalized oxindoles has been accomplished by the groups of Lei, [7d] Zeng, [7e] Mo, [7g] and other groups (Scheme 1 a). Also, addition of various carbon or phosphorous [8] radicals, including fluorinated ones, [8c] to the same 2‐Ph indoles N‐substituted by an acryloyl group is known to be promoted by electrochemistry, [8a] visible light, [8b,c] or stoichiometric oxidants [8d, e] . The difference with the present work is that the oxidative cleavage of the indole does not occurs in these previous reports.…”

Transition Metal‐Free Synthesis of Sulfonyl‐ and Bromo‐Substituted Indolo[2,1‐α]isoquinoline Derivatives through Electrochemical Radical Cascade Cyclization

“…Recently, Xu and co‐workers described the synthesis of indolo[2,1‐α]isoquinoline core structures under visible‐light‐promoted conditions [8] . In their developed system, acyl radicals were generated from benzoyl chlorides and added to 2‐aryl‐ N ‐acryloyl indoles, which triggered the radical cascade cyclization process (Scheme 1a).…”

“…All the starting materials are known compounds. They can be synthesized according to the published methods [8,9] …”

“…Replacing the Pt anode with a graphite rod led to a dramatic drop in the yield of 3 a (entry 6). Moreover, other solvent systems were explored but provided no improvement over THF/H 2 O (entries [7][8][9][10][11]. Notably, the yield of 3 a was slightly reduced when 2.0 equiv.…”

Synthesis of Indolo[2,1‐a]isoquinolin‐6(5H)‐Ones Derivatives via Fe(OTf)3‐Promoted Tandem Selenylation/Cyclization of 2‐Arylindoles

“…It is the simple and convenient approach to prepare indolo[2,1‐a]isoquinli‐ne derivatives containing the tetracyclic core by using 2‐arylindoles as materials, and all the reported methods to indolo[2,1‐a]isoquinoline derivatives containing the tetracyclic core involving a radical cyclization process. For example, Xu's group developed a photocatalyzed transformation for the synthesis of indolo[2,1‐a]isoquinoline derivatives from 2‐arylindoles and acyl chloride [7] . Yu's group reported a metal‐free visible‐light‐induced radical cyclization procedure for the synthesis of perfluoroalkyl‐substituted indolo[2,1‐ a ]isoquinolin‐6(5 H )‐ones [8] .…”