Cascades to Substituted Indoles

Abstract

This paper describes the synthesis of dithioindoles from the free-radical cyclizations of arylisonitriles having pendant alkynes. Also described is the synthesis of substituted indoles and spiro-fused indoles from the coupling of dithioindoles with active hydrogen-containing compounds.

Recent advances in sulfur- and phosphorous-centered radical reactions for the formation of S–C and P–C bonds

“…Rainier and Kennedy reported the reaction of alkynyl arylisonitrile 157 with sulfenyl radicals for the synthesis of dithioindoles 158 (Scheme 71) 129. to form 160 (38%), 161 (26%), and 162 (6%) from the reaction mixture (Scheme 72) 130.…”

Aliphatic aldehydes in the synthesis of carbo- and heterocycles. Part I. Synthesis of three-, four-, and five-membered rings

“…The reactions with α,β-unsaturated ketones smoothly occur in the absence of a catalyst, which may be regarded as an evidence in support of the proposed mechanism. New spiro pyrroles 61 were obtained by the Piktet-Spengler reaction under mild conditions [67] α-Isonitroso ketones 62 derived from tetrahydrobenzofurazan and furoxan reacted with aldehyde 9a or 9j and morpholine (63) to give fused dihydropyrrole N-oxide derivatives 64 [68] (Scheme 25). A classical method for the synthesis of indoles is the Fischer reaction whose mechanism was studied in sufficient detail [69].…”

Catalytic Synthesis of Indoles from Alkynes

“…Based on the Fukayama isonitrile-alkene free-radical coupling reaction, [55] the group of Rainier developed an analogous alkyne-isonitrile free-radical reaction for the synthesis of indoles (Scheme 30). [56] Starting from aryl isocyanides having a suitably positioned alkyne, 5-exo-dig radical cyclization provided the indolenine intermediate 100. The resulting 2-stannylindole can be destannylated by acidic workup to afford the 3-substituted indole 101.…”