Visible‐Light‐Mediated Nitrogen‐Centered Radical Strategy: Preparation of 3‐Acylated Spiro[4,5]trienones

Abstract

A nitrogen‐centered radical strategy for the preparation of 3‐acylated spiro[4,5]trienones via visible‐light‐mediated acylation/ipso‐cyclization of alkynes with acyl oxime esters is reported. The alkyl‐ and aryl‐substituted acyl radicals, which generate from the cleavage of carbon‐carbon σ‐bonds in acyl oxime esters via nitrogen‐centered radical pathway, attack the carbon‐carbon triple bonds in propiolamides and then undergo ipso‐cyclization. This method provides a way for the construction of 3‐acyl‐substituted spiro[4,5]trienones, which can introduce aryl‐ or alkyl‐substituted acyl into spiro[4,5]trienone skeletons.

Visible-Light-Induced Transition-Metal-Free Nitrogen-Centered Radical Strategy for the Synthesis of 2-Acylated 9H-Pyrrolo[1,2-a]indoles

“…According to the above experimental and literature results, ,,,, the possible mechanism of visible-light-induced transition-metal-free tandem acylation/cyclization of N -propargylindoles with acyl oxime esters was proposed (Scheme ). First, Eosin Y was excited by visible light to form a strong reducing agent, Eosin Y*. − Then, acyl oxime ester 2a underwent the single electron transfer with Eosin Y*, followed by reduction quenching to obtain iminyl radical A along with the Eosin Y •+ radical cation.…”

“…Oxime esters are an important class of NCR precursors, which are usually applied to construct useful and functional compounds in organic chemistry . In recent years, acyl oxime esters were employed as facile acylation reagents in acylation reactions . In these transformations, the highly active iminyl radicals, which formed through thermal activation, transition-metal catalysis, or photo irradiation , by cleavage of the nitrogen–oxygen bond in oxime esters, could undergo a β-fragmentation to form acyl radicals along with generating the corresponding nitriles.…”

Visible‐Light‐Induced Acylation/Arylation of Alkenes via Aryl Migration/Desulfonylation

“…Acyl oxime esters could be reduced through single electron transfer in the presence of photocatalyst to yield highly reactive iminyl radicals, which underwent β‐C−C bond fragmentation to disconnect acyl radicals from iminyl radicals through elimination of a nitrile molecule (Scheme 1c). The resulting acyl radicals could be coupled with a wide range of radical acceptors, including alkenes, [15a–c] aromatic rings, [15d] and alkynes [15e–g] . For example, Wu and co‐workers reported a photocatalytic acyl radical cascade reaction between acyl oxime esters with acrylamides and styrenes, respectively [15a] .…”

“…In 2020, Yang and co‐workers achieved a phosphoranyl‐radical‐promoted the hydroacylation of alkenes using acyl oximes as acyl radical source under photocatalytic conditions, which provides a facile route toward valuable ketones synthesis [15c] . Recently, our group reported the visible‐light‐induced acyl radical transfer followed by cyclization reactions using alkynes‐containing molecule as reactants including propiolamides, [15e] N ‐propargylindoles, [15f] and alkynoates [15g] as the radical acceptors. With our continuing interests in the development of oxime esters involved organic transformations under photoredox catalysis, [15e–f,16] we herein reported the radical cascade reaction [17] of N ‐tosyl acrylamide [18] with acyl oxime esters to prepare acylated indolin‐2‐ones through a tandem acyl radical addition/aryl migration [19] /desulfonylation/cyclization process on the basis of NCR strategy (Scheme 2).…”

Difunctionalization of Dienes, Enynes and Related Compounds via Sequential Radical Addition and Cyclization Reactions

“…Scheme 92 shows another example of the reaction of N -( p -methoxyaryl)-propiolamides developed by Liu’s group also for the synthesis of 3-acylspiro[4,5]trienones [ 102 ].The photoredox reaction of alkynes, acyl oxime esters, H 2 O under the catalysis of Ir(ppy) 3 gave product 92 in good yields.…”