Recent advances in radical transformations of internal alkynes

Abstract

Over the past years, impressive progress has been made on the development of the chemoselective and direct formation of carbon-carbon and carbon-heteroatom bonds involving internal alkynes under catalytic oxidative systems. These transformations heavily rely on the in situ generation of reactive radical intermediates that are initiated by oxidants, visible light photocatalysis, or electrocatalysis and so on. Numerous chemically and biomedically important building blocks have been synthesized, and will continue to be obtained by taking advantage of the radical transformation of internal alkynes in the following years. In this review, we highlight the recent progress in this rapidly growing area by presenting a series of catalytic oxidative reactions, mechanisms and applications which have appeared in the most recent literature.

Cu‐Catalyzed [4+1] Annulation toward Indolo[2,1‐a]isoquinolines through Oxidative C(sp3)/C(sp2)−H Bond Bifunctionalization

“…On the other hand, developmento fp ractical and sustainable synthetic methods for the rapid construction of valuable cyclic target molecules, along with minimum environmental impacts, represents an endeavor of utmost importance in both academia and industry. [7] In the context,d irect CÀHb ond functionalizationt hat allows the straightforward conversion of CÀH bondst oC ÀCb onds has been recognized as as tep-and atom-economic synthetic strategy for the assembly of bioactive moleculess ince such transformation could avoid the time and cost consuming prefunctionalization. [8] However,d irect functionalization of inactive C(sp 3 )ÀHo rC (sp 2 )ÀHb onds in a predictable manner is more challenging due to the low polarity.…”

Silver‐Catalyzed Nitration/Annulation of α‐Alkynyl Arylols toward 3‐Nitrated Benzofurans

“…Recently, our group reported a silver‐catalyzed nitration‐annulation of 2‐alkynylanilines with TBN, leading to the selective generation of a variety of C5/7‐nitroindoles (Scheme , path a) . However, NO 2 radical‐triggered difunctionalization of internal alkynes remains almost unexplored, probably because of their strong bond energy and difficulty in the regioselectivity …”

“…[5] However,N O 2 radical-triggered difunctionalization of internal alkynesr emains almostu nexplored, [6] probably because of their strong bond energy and difficulty in the regioselectivity. [7] One the other hand, benzofurans are an important structural scaffold in the pharmaceutical application and have exhibited aremarkable biological and pharmacological activities. [8] For instance,3 -nitrobenzofurans have been found to show antibacterial, parasiticidal [9] anda ntimicrobial [10] activities.…”

“…In contrast, the yield of 2a remarkably decreasedw hen the temperature was raised to 25 8C( entry 4). As the next optimization step, we examined the solvent effect by adjusting reaction media, including 1,4-dioxane, toluene, dimethylformamide (DMF), dichloroethane (DCE) and acetonitrile (entries [5][6][7][8][9]. After carful screening of these solvents, we found that 1,4-dioxane was provent ob et he best one, affording 2a in 50 %yield (entry 5).…”

Atom Transfer Oxidative Radical Cascade of Aryl Alkynoates towards 1,1‐Dichalcogenide Olefins

“…[1] In this context,a ryl alkynoates encompassing activated alkyne functionality serve as valuableb uildingb locks. [1] In this context,a ryl alkynoates encompassing activated alkyne functionality serve as valuableb uildingb locks.…”