Direct photocatalytic coupling of methanol to ethylene glycol(EG)is highly attractive.The reported photocatalysts for this reaction are all metal sulfide semiconductors,which may suffer from photocorrosion and have lo...Direct photocatalytic coupling of methanol to ethylene glycol(EG)is highly attractive.The reported photocatalysts for this reaction are all metal sulfide semiconductors,which may suffer from photocorrosion and have low stability.Thus,the development of non‐sulfide photocatalysts for efficient photocatalytic coupling of methanol to EG and H2 with high stability is urgent but extremely challenging.Herein,the first metal oxide photocatalyst,tantalum‐based semiconductor,is reported for preferential activation of C−H bond within methanol to form hydroxymethyl radical(•CH_(2)OH)and subsequent C−C coupling to EG.Compared with other metal oxide photocatalysts,such as TiO2,ZnO,WO_(3),Nb_(2)O_(5),tantalum oxide(Ta_(2)O_(5))is unique in that it can realize the selective photocatalytic coupling of methanol to EG.The co‐catalyst free nitrogen doped tantalum oxide(2%N‐Ta_(2)O_(5))shows an EG formation rate as high as 4.0 mmol gcat−1 h−1,about 9 times higher than that of Ta_(2)O_(5),with a selectivity higher than 70%.The high charge separation ability of nitrogen doped tantalum oxide plays a key role in its high activity for EG production.This catalyst also shows excellent stability longer than 160 h,which has not been achieved over the reported metal sulfide photocatalysts.Tantalum‐based photocatalyst is an environmentally friendly and highly stable candidate for photocatalytic coupling of methanol to EG.展开更多
Aromatic oxazolines are versatile in organic synthesis as directing groups,ligands,and protected carboxylic acids.Developing efficient approaches to oxazoline from an aromatic C−H bond is more desirable compared to th...Aromatic oxazolines are versatile in organic synthesis as directing groups,ligands,and protected carboxylic acids.Developing efficient approaches to oxazoline from an aromatic C−H bond is more desirable compared to the established protocols from carboxylic acid and its equivalents.Herein,a simple and efficient aromatic C−H oxazolination with broad substrate scope is described.By employing this transformation as an enabling step,diversity-oriented synthesis of functionalized arenes and target-oriented synthesis of four drugs were accomplished.Mechanistic experiments suggest that this aromatic oxazolination is an electrophilic aromatic substitution.It is anticipated that this transformation will find applications in aromatic C−H functionalization with oxazoline either as a removable directing group or as a masked carboxylic acid.展开更多
While electrocatalyzed alkyne annulations of arenes represent a powerful strategy for the assembly of heteroaromatic motives,electrochemical C(sp2)−H activations of alkenes remain scarce.Herein,a strategy for the rhod...While electrocatalyzed alkyne annulations of arenes represent a powerful strategy for the assembly of heteroaromatic motives,electrochemical C(sp2)−H activations of alkenes remain scarce.Herein,a strategy for the rhodaelectro-catalyzed function-alization of enamides is presented for the efficient construction of pyrroles using electricity as a sustainable oxidant.Moreover,the tuning of the solvent system allowed a fascinating switch in chemoselectivity,which is not possible with traditionally used chemical oxidants,giving rise to lactone architectures.The rhoda-electrocatalysis features a broad scope as well as high regio-and chemoselectivities.展开更多
The C2-α-mannosyl-tryptophan amino acid is produced by a unique posttranslational modification(PTM)of proteins and poses a significant synthetic challenge.A new strategy based on Pd-catalyzed auxiliary-directed remot...The C2-α-mannosyl-tryptophan amino acid is produced by a unique posttranslational modification(PTM)of proteins and poses a significant synthetic challenge.A new strategy based on Pd-catalyzed auxiliary-directed remote C-H glycosylation of tryptophan was developed,which generates the C2-α-mannopyranose(Man)-Trp unit in a highly efficient and stereoselective fashion.Density functional theory(DFT)computational studies support a concerted oxidative addition mechanism for the stereospecific functionalization of a Pd(II)palladacycle intermediate with anα-mannosyl chloride donor.The utility of this method was demonstrated in the first total synthesis of insect C-glycopeptide hormone Cam-HrTH-I.展开更多
Ligands can definitely influence C−H activation at the metal center.A ligand not directly participating in the reaction is called a spectator ligand.We attempt to quantitatively characterize the effects of diverse spe...Ligands can definitely influence C−H activation at the metal center.A ligand not directly participating in the reaction is called a spectator ligand.We attempt to quantitatively characterize the effects of diverse spectator ligands on C−H activation at palladium.We designed a model palladium catalyst and selected an array of spectator ligands,such as methoxyl,amide,methyl,phenyl,cyanide,fluorine,chlorine,and several neutral ligands,and performed density functional theory calculations on the mechanism and energetics of C−H activation reactions of benzene with different catalysts.Univalent ligands have substantially larger effects than neutral ligands,and stronglyσ-donating ligands(e.g.,methyl and phenyl)severely hinder the C−H activation in progress.A ligand trans to the reaction site influences C−H activation more than that cis to the reaction site,indicating electronic effects to be at work.For example,the existence of a methyl ligand raises the barrier height of C−H activation by 6.4 or 14.4 kcal/mol when it is placed at the position cis or trans to the C−H activation site.The effects of poorlyσ-donating ligands are not significant and similar to those of theκ1-acetate ligand.Someσ-donating andπ-accepting ligands,such as cyanide and isonitrile,hinder the C−H activation trans to them but appear to facilitate the C−H activation cis to them.On the basis of molecular orbital analyses,a chemical model is proposed to understand the observed ligand effects.Lastly,the conclusions are applied to explain the plausible mechanism of the dehydrogenative Heck coupling.展开更多
Heterogenization of organic-macrocyclic metal catalysts is one of the simplest and most efficient methods for effective separation of products and cyclic application of a catalyst.By using an environmentally friendly ...Heterogenization of organic-macrocyclic metal catalysts is one of the simplest and most efficient methods for effective separation of products and cyclic application of a catalyst.By using an environmentally friendly Mn-corrolazine catalyst as the building unit,which can directly oxidize organic substrates under oxygen atmosphere and mild conditions,we theoretically constructed a novel two-dimensional(2D)Mn-corrolazine nanocatalytic material with high catalytic activity.In this material,each Mn atom maintains its electronic configuration in the monomer and can directly activate O2 as the single-atom catalyst(SAC)center to form a radical-like[Mn]-O-O under mild visible-light irradiation conditions.The newly generated[Mn]–O–O can efficiently and selectively oxidize C–H bonds to form alcohol species through H-abstraction and the rebound reaction.Moreover,the catalytic reaction is easily regulated by an external electric field along its intrinsic Mn–O–O reaction axis.The current study provides a theoretical foundation for further experimental studies and practical applications of the Mn-corrolazine-based SAC.展开更多
文摘Direct photocatalytic coupling of methanol to ethylene glycol(EG)is highly attractive.The reported photocatalysts for this reaction are all metal sulfide semiconductors,which may suffer from photocorrosion and have low stability.Thus,the development of non‐sulfide photocatalysts for efficient photocatalytic coupling of methanol to EG and H2 with high stability is urgent but extremely challenging.Herein,the first metal oxide photocatalyst,tantalum‐based semiconductor,is reported for preferential activation of C−H bond within methanol to form hydroxymethyl radical(•CH_(2)OH)and subsequent C−C coupling to EG.Compared with other metal oxide photocatalysts,such as TiO2,ZnO,WO_(3),Nb_(2)O_(5),tantalum oxide(Ta_(2)O_(5))is unique in that it can realize the selective photocatalytic coupling of methanol to EG.The co‐catalyst free nitrogen doped tantalum oxide(2%N‐Ta_(2)O_(5))shows an EG formation rate as high as 4.0 mmol gcat−1 h−1,about 9 times higher than that of Ta_(2)O_(5),with a selectivity higher than 70%.The high charge separation ability of nitrogen doped tantalum oxide plays a key role in its high activity for EG production.This catalyst also shows excellent stability longer than 160 h,which has not been achieved over the reported metal sulfide photocatalysts.Tantalum‐based photocatalyst is an environmentally friendly and highly stable candidate for photocatalytic coupling of methanol to EG.
基金the Fundamental Research Funds for the Central Universities(22qntd2306)Guangzhou Municipal Science and Technology Bureau(202201011151)the National Natural Science Foundation of China(22201311).
文摘Aromatic oxazolines are versatile in organic synthesis as directing groups,ligands,and protected carboxylic acids.Developing efficient approaches to oxazoline from an aromatic C−H bond is more desirable compared to the established protocols from carboxylic acid and its equivalents.Herein,a simple and efficient aromatic C−H oxazolination with broad substrate scope is described.By employing this transformation as an enabling step,diversity-oriented synthesis of functionalized arenes and target-oriented synthesis of four drugs were accomplished.Mechanistic experiments suggest that this aromatic oxazolination is an electrophilic aromatic substitution.It is anticipated that this transformation will find applications in aromatic C−H functionalization with oxazoline either as a removable directing group or as a masked carboxylic acid.
基金Generous support from ERC Advanced Grant 101021358 and the DFG Gottfried Wilhelm Leibniz award(L.A.)is gratefully acknowledged.E.R.thanks the Basque Government(Grupos IT1558-22)for financial support.
文摘While electrocatalyzed alkyne annulations of arenes represent a powerful strategy for the assembly of heteroaromatic motives,electrochemical C(sp2)−H activations of alkenes remain scarce.Herein,a strategy for the rhodaelectro-catalyzed function-alization of enamides is presented for the efficient construction of pyrroles using electricity as a sustainable oxidant.Moreover,the tuning of the solvent system allowed a fascinating switch in chemoselectivity,which is not possible with traditionally used chemical oxidants,giving rise to lactone architectures.The rhoda-electrocatalysis features a broad scope as well as high regio-and chemoselectivities.
基金The experimental studies of this work were funded by NSFC-91753124,NSFC-21672105,NSFC-21421062,and NSFC-21725204 grants.
文摘The C2-α-mannosyl-tryptophan amino acid is produced by a unique posttranslational modification(PTM)of proteins and poses a significant synthetic challenge.A new strategy based on Pd-catalyzed auxiliary-directed remote C-H glycosylation of tryptophan was developed,which generates the C2-α-mannopyranose(Man)-Trp unit in a highly efficient and stereoselective fashion.Density functional theory(DFT)computational studies support a concerted oxidative addition mechanism for the stereospecific functionalization of a Pd(II)palladacycle intermediate with anα-mannosyl chloride donor.The utility of this method was demonstrated in the first total synthesis of insect C-glycopeptide hormone Cam-HrTH-I.
基金supported by the National Natural Science Foundation of China (22003045, 21808156)the Fundamental Research Funds for Tianjin Colleges (2018KJ171, 2017KJ064)the High-performance Computing Platform of Tianjin Chengjian University
文摘Ligands can definitely influence C−H activation at the metal center.A ligand not directly participating in the reaction is called a spectator ligand.We attempt to quantitatively characterize the effects of diverse spectator ligands on C−H activation at palladium.We designed a model palladium catalyst and selected an array of spectator ligands,such as methoxyl,amide,methyl,phenyl,cyanide,fluorine,chlorine,and several neutral ligands,and performed density functional theory calculations on the mechanism and energetics of C−H activation reactions of benzene with different catalysts.Univalent ligands have substantially larger effects than neutral ligands,and stronglyσ-donating ligands(e.g.,methyl and phenyl)severely hinder the C−H activation in progress.A ligand trans to the reaction site influences C−H activation more than that cis to the reaction site,indicating electronic effects to be at work.For example,the existence of a methyl ligand raises the barrier height of C−H activation by 6.4 or 14.4 kcal/mol when it is placed at the position cis or trans to the C−H activation site.The effects of poorlyσ-donating ligands are not significant and similar to those of theκ1-acetate ligand.Someσ-donating andπ-accepting ligands,such as cyanide and isonitrile,hinder the C−H activation trans to them but appear to facilitate the C−H activation cis to them.On the basis of molecular orbital analyses,a chemical model is proposed to understand the observed ligand effects.Lastly,the conclusions are applied to explain the plausible mechanism of the dehydrogenative Heck coupling.
文摘Heterogenization of organic-macrocyclic metal catalysts is one of the simplest and most efficient methods for effective separation of products and cyclic application of a catalyst.By using an environmentally friendly Mn-corrolazine catalyst as the building unit,which can directly oxidize organic substrates under oxygen atmosphere and mild conditions,we theoretically constructed a novel two-dimensional(2D)Mn-corrolazine nanocatalytic material with high catalytic activity.In this material,each Mn atom maintains its electronic configuration in the monomer and can directly activate O2 as the single-atom catalyst(SAC)center to form a radical-like[Mn]-O-O under mild visible-light irradiation conditions.The newly generated[Mn]–O–O can efficiently and selectively oxidize C–H bonds to form alcohol species through H-abstraction and the rebound reaction.Moreover,the catalytic reaction is easily regulated by an external electric field along its intrinsic Mn–O–O reaction axis.The current study provides a theoretical foundation for further experimental studies and practical applications of the Mn-corrolazine-based SAC.
