ortho‐Oxygenative 1,2‐Difunctionalization of Diarylalkynes under Merged Gold/Organophotoredox Relay Catalysis

Abstract

Reported herein is an ortho-oxygenative 1,2-difunctionalization of diarylalkynes under mergedg old/organophotoredox catalysis to access highly functionalized 2-(2-hydroxyaryl)-2-alkoxy-1-arylethan-1-ones.Detailed mechanistic studies suggested ar elay process, initiating with gold-catalyzed hydroalkoxylationo fa lkynes, to generate enol-ether followed by ak ey formal [4+ +2]-cycloaddition reaction. Thes uccessful application of the present methodologyw as also shown for the synthesis of benzofurans.

Metallaphotoredox: The Merger of Photoredox and Transition Metal Catalysis

“…Thereafter, calculations suggest several possible mechanisms of activation of iodoalkyne electrophile 309 by excited-state Au­(I) complex 310 , which ultimately leads to the desired alkynylated benzofuran. Patil and co-workers leveraged a similar energy-transfer mechanism in a dual gold/organophotoredox platform toward the ortho -oxygenative 1,2-difunctionalization of diarylalkynes to access highly functionalized 2-(2-hydroxyaryl)-2-alkoxy-1-arylethan-1-ones, as well a benzofurans . Energy transfer from photoexcited Eosin Y generates a necessary singlet oxygen to undergo a formal [4+2] cycloaddition with an enol ether generated in situ via gold-catalyzed hydroalkoxylation.…”

Eosin: a versatile organic dye whose synthetic uses keep expanding

“…Here, excited state eosin most frequently acts as an oxidant (*EY → EY •− , Scheme 37A-E), [57][58][59][60][61] but there is also an example where it is acting as a reductant (*EY → EY •+ , Scheme 37F) 62 and one where it acts as an energy transfer agent to generate singlet oxygen (Scheme 37G). 63 An important application of this concept within the critical fields of green chemistry and clean energy chemistry (hydrogen production) was recently reported by the group of Kim. 64 In this investigation, a bio-inspired nickel catalyst with eosin as cooxidant was used to fix carbon dioxide to produce formate ions.…”

“…Eosin's versatility is very well showcased in this section about cooperative catalysis being used for the synthesis of privileged scaffolds. In these examples that are summarized in Scheme 37, [57][58][59][60][61][62][63] eosin is acting in consort with a transition metal to complete the requisite catalytic cycles. Eosin facilitates the use of mild conditions and can widen functional group tolerance.…”

Last Decade of Unconventional Methodologies for the Synthesis of Substituted Benzofurans

“…A new method to generate o-hydroxybenzyl ketones was proposed recently by Patil and co-workers, using an o-oxygenative 1,2-difunctionalization of diarylalkynes. This procedure allowed under merged gold/organophotoredox catalysis to access highly functionalized 2-(2-hydroxyaryl)-2-alkoxy-1-arylethan-1-ones [76]. Detailed mechanistic studies suggested a relay process, initiating with gold-catalyzed hydroalkoxylation of alkynes, to generate enol-ether followed by a key formal [4 + 2]-cycloaddition reaction.…”