Direct Photoexcitation of Ethynylbenziodoxolones: An Alternative to Photocatalysis for Alkynylation Reactions**

Abstract

Ethynylbenziodoxolones (EBXs) are commonly used as radical traps in photocatalytic alkynylations. Herein, we report that aryl‐substituted EBX reagents can be directly activated by visible light irradiation. They act as both oxidants and radical traps, alleviating the need for a photocatalyst in several reported EBX‐mediated processes, including decarboxylative and deboronative alkynylations, the oxyalkynylation of enamides and the C−H alkynylation of THF. Furthermore, the method could be applied to the synthesis of alkynylated quaternary centers from tertiary alcohols via stable oxalate salts and from tertiary amines via aryl imines. A photocatalytic process using 4CzIPN as an organic dye was also developed for the deoxyalkynylation of oxalates.

Updates on hypervalent-iodine reagents: metal-free functionalisation of alkenes, alkynes and heterocycles

“…Deoxyalkynylation of caesium oxalates ( 37 ) required photocatalytic conditions and their best-optimised conditions and the scope of this reaction were explored which resulted in the successful formation of the alkynylated products ( 38 ) with good yields (Scheme 23). 75…”

“…Deoxyalkynylation of caesium oxalates (37) required photocatalytic conditions and their best-optimised conditions and the scope of this reaction were explored which resulted in the successful formation of the alkynylated products (38) with good yields (Scheme 23). 75 Recently, the Chen group reported aminoalkyne (40) synthesis from selective C(sp 3 )-C(sp 3 ) cleavage/alkynylation of cycloalkylamides (39) under mild photoredox catalysis. An array of γand δ-aminoalkynes containing diverse alkyne and amine substituents are efficiently constructed from cyclopropylamides and cyclobutylamides via amidyl radicals facilitated by HVI(III) reagents.…”

Radical Deoxyfunctionalisation Strategies**

“…Similarly, Waser recently developed an alternative approach for the alkynylation of oxalates using ArEBX reagents 69 as radical traps (Scheme 36). [57] Excitation of these reagents gives ArEBX* (70), which can be used as an effective photooxidant to activate numerous oxidizable species (e. g. carboxylates, alkyl trifluoroborates, electron-rich aromatics). Under the standard optimised conditions, this unique methodology allowed for the deoxyalkynylation of a wide range of aliphatic tertiary caesium oxalates in good yields.…”

New Approaches toward Building Csp−P bond: A Two‐Decade Overview

“…Alkynyl(phenyl)iodonium salts have attracted substantial interest as effective alkynylating reagents. [86][87][88] They can be used in various coupling organometallic and photoredox-catalyzed reactions [89] or be reacted with a large set of nucleophilic species. [90][91][92] In 1990, Koser and co-workers treated various alkynyl(phenyl)iodonium tosylates 140 by an excess of neat trialkyl phosphites 139 as nucleophiles (Scheme 56a).…”