Dual Cobalt And Photoredox Catalysis Enabled Annulation Of 2-propynolphenols

In recent years,visible-light-induced photoredox catalysis has attracted extensive attention due to its green,mild,and sustainable properties.Numerous chemical transformations of small molecules can be realized under mild conditions by converting visible into chemical energy.Among them,the combination of photoredox catalysis and transition-metal catalysis to develop novel catalytic reaction is an important aspect of photochemical research,and it is also significant content of organometallic chemistry.Cobalt（Co）is earth-abundant,inexpensive,and low toxic.It can exist in a variety of oxidation states（0,+1,+2,+3）and engage both in one-electron and two electron redox processes.And the low cobalt can easily capture proton to afford cobalt-hydride species,which can trigger diverse organic transformations.The oxidation state of cobalt could be feasible manipulated via single electron transfer process,and further reacted with proton（H⁺）to generate key Co-H intermediates,which in turn lead to a variety of novel organic chemical reactions.This has increasingly become a research hotspot in the field of cobalt catalysis.Based on the characteristics of photoredox/cobalt catalysis,this article focused on the research of cyclization process of 2-propynolphenols via dual catalytic system,which constructed a series of dihydrobenzofuran and benzofuran derivatives with high efficiency and selectivity.Meanwhile,the mechanism was invested and the inherent laws of this type of reaction were revealed.The specific research contents are as follows:1.We developed a reaction of hydroxyl assisted,photoredox/cobalt cocatalyzed semi-hydrogenation and tandem intramolecular hydroetherification of alkene in one-pot manipulation for direct construction of 2,3-dihydrobenzofurans from 2-propynolphenols.Mechanistic studies suggested that the reaction may involve a tandem process of photo-induced Co-H species catalyzed semi-hydrogenation of alkynes and low-valent cobalt catalyzed phenolic O-H activation to achieve cyclization.2.A hydroxyl-assisted,photoredox/cobalt dual catalyzed annulation of 2-propynolphenols to from 2-hydroxymethyl-benzo[b]furans were developed by employing organic dye 4Cz IPN as photosensitizer and CoCl₂（PPh₃）₂/5,5’-dimethyl-2,2’-bipyridine as cobalt catalytic precursor.In addition,the 2-hydroxybenzofuran derivatives can be further subjected to Br（?）nsted acid-catalyzed highly regioselective C1 or C3 phosphorylation or indole derivatization reactions.Primary mechanistic studies suggested the involvement of cobalt-hydride mediated hydrogen atom transfer（HAT）process.3.Based on the above research,we explore actively photoredox/cobalt dual catalyzed reduction of 1,2-dicarbonyl compounds.A photocatalyst-and metal-free platform for the photoreduction of 1,2-dicarbonyl compounds was developed.A series ofα-hydroxy ketone/ester derivatives were synthesized under mild conditions.Experimental studies and DFT calculations support a double hydrogen atom transfer（HAT）pathway.