Eosin Y photoredox catalyzed net redox neutral reaction for regiospecific annulation to 3-sulfonylindoles via anion oxidation of sodium sulfinate salts

Abstract

An eosin Y photoredox catalyzed net redox neutral process for 3-sulfonylindoles via the anionic oxidation of sodium sulfinate salts and its radical cascade cyclization with 2-alkynyl-azidoarenes was developed with visible light as a mediator. The reaction offers metal and oxidant/reductant free, visible light mediated vicinal sulfonamination of alkynes to 2-aryl/alkyl-3-sulfonylindoles and proceeds via the generation of a sulfur-centered radical through direct oxidation of the sulfinate anion by an excited photocatalyst with a reductive quenching cycle. The mild conditions, use of an organic dye as photo-catalyst, bench stability and easily accessible starting materials make the present approach green and attractive.

Photoredox-catalyzed branch-selective pyridylation of alkenes for the expedient synthesis of Triprolidine

“…Design plan. We hypothesized that sodium sulfinates would be the ideal reusable radical precursors, due to the unique properties of which: (i) sufinates have been recently employed as efficient sulfonyl coupling partners in photoredox catalysis [47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] ; (ii) it is well known that the alkyl sulfones would be prone to undergo desulfonylation under basic conditions [63][64][65] . As depicted in Fig.…”

Synthesis and applications of sodium sulfinates (RSO2Na): a powerful building block for the synthesis of organosulfur compounds

“…A radical cascade ringclosing sulfonylation of 2-alkynyl-azido-arenes was developed by Kshirsagar and co-workers (Scheme 206). 313 The substrate scope of 2alkynyl-azido-arenes treated with sodium benzenesulnate and proceeded well to the 3-sulfonylindoles in good to high yields. Moreover, a variety of aromatic and aliphatic sulnate salts were subjected to 1azido-2-(phenylethynyl)benzene and proceeded smoothly to deliver the corresponding products in 43-73% yields.…”

Recent Progress in Sulfonylation via Radical Reaction with Sodium Sulfinates, Sulfinic Acids, Sulfonyl Chlorides or Sulfonyl Hydrazides

“…In 2018, the visible light induced regiospecific annulation of 2‐alkynyl‐azidoarenes with sodium sulfinates for the synthesis of 2‐aryl/alkyl‐3‐sulfonyl‐indoles was developed by Kshirsagar group [36] . The generation of sulfonyl radical through direct oxidation of the sulfinate anion by the excited photocatalyst via reductive quenching cycle was involved in the reaction mechanism (Scheme 28).…”