Synthesis of Alkylsulfonyl‐Substituted Indolo[2,1‐a]Isoquinolines via Photoredox‐Catalyzed Radical‐Cascade Addition/Sulfonylation/Cyclization with DABCO ⋅ (SO₂)₂ and Thianthrenium Salts

Abstract

A direct, visible‐light‐mediated, radical‐cascade addition/sulfonylation/cyclization reaction with DABCO ⋅ (SO2)2 and thianthrenium salts is reported herein. This protocol provides operationally‐convenient access to various sulfonated functionalized indole [2,1‐a] isoquinolines under mild conditions. This transformation features high functional‐group tolerance, operational ease, and broad substrate scope. Preliminary studies reveal that the method undergoes a radical pathway.

Visible‐Light‐Driven Sulfonamidation of Arylazo Sulfonesthrough One‐Pot Multicomponent Reaction

“…Based on the control experiments and the previously published literatures, [40][41][42][43][44][45] a plausible mechanism for this visible-light-induced multicomponent transformation is pro-…”

“…Based on the control experiments and the previously published literatures, [40–45] a plausible mechanism for this visible‐light‐induced multicomponent transformation is provided (Scheme 4). With irradiation of blue LED light, aryl radical II is generated via activation of arylazo sulfone 1 a , followed by homolytic scission of the N−S linkage (1nπ* excited state).…”

“…[30][31][32][33][34][35][36][37][38] However, photochemical reactions often require expensive photocatalysts such as complexes of Ir or Ru metals or dye compounds. [39][40][41][42] Therefore, it is useful to develop novel photocatalyst-free photochemical reactions.…”

“…Typically, photochemical methods are effectively used for reactions involving radical pathways to form C−C coupling or carbon‐heteroatom bonds [30–38] . However, photochemical reactions often require expensive photocatalysts such as complexes of Ir or Ru metals or dye compounds [39–42] . Therefore, it is useful to develop novel photocatalyst‐free photochemical reactions.…”

Organophotocatalytic cascade cyclization reactions for the synthesis of cyanoalkyl indole[2,1-a]isoquinolinones

“…1 As a result, tremendous efforts have been devoted to synthesizing structurally diverse indolo[2,1- a ]isoquinolinones. Recently, cascade cyclization of 2-aryl- N -methacryloyl indoles has been regarded as a useful tool for the preparation of various indolo[2,1- a ]isoquinoline derivatives, in which C–C, 2 C–N, 3 C–S 4 and C–X 5 bond functionalized indolo[2,1- a ]isoquinolines have been successfully constructed. For instance, Qiu's group reported a visible-light photocatalytic radical cyclization reaction to access tri- and difluoroalkylation indole[2,1- a ]isoquinoline derivatives in continuous flow.…”