碳纳米管负载铂催化剂的制备、结构及电化学加氢特性

采用浸渍沉淀法制备Pt/CNTs和Pt/C催化剂,并对其结构及电催化性能进行比较,表征.实验表明,以碳纳米管作催化剂载体可使催化剂的负载量,载体上铂的分散度以及其活性中心大大提高.与Pt/C(JohnsonMatthey)催化剂相比,Pt/CNTs的电化学性能表现出更大的活性.碳纳米管作为阴极材料在质子交换膜燃料电池加氢反应器合成化学品中的作用十分明显.     

Organocatalytic Asymmetric 1,6‐Addition/1,4‐Addition Sequence to 2,4‐Dienals for the Synthesis of Chiral Chromans

A novel asymmetric organocatalytic 1,6‐addition/1,4‐addition sequence to 2,4‐dienals is described. Based on a 1,6‐Friedel–Crafts/1,4‐oxa‐Michael cascade, the organocatalyst directs the reaction of hydroxyarenes with a vinylogous iminium‐ion intermediate to give only one out of four possible regioisomers, thus providing optically active chromans in high yields and 94–99 % ee. Furthermore, several transformations are presented, including the formation of an optically active macrocyclic lactam. Finally, the mechanism for the novel reaction is discussed based on computational studies.     

聚合物负载贵金属催化剂的合成及其在氢化反应中的应用进展

聚合物负载贵金属催化剂大多具有良好的光学催化活性,并且反应后容易从反应物中分离,重复实用性高,成为近年来人们研究的热点。常见的聚合物载体主要为有机聚合物及多种无机-有机杂化材料。本文主要按聚合物载体种类的不同,综述了聚合物负载Pt、Pd、Rh等贵金属催化剂的制备方法及其在烯烃、二烯烃、炔烃和硝基芳香化合物等物质的催化氢化中的应用情况。同时,对以树形分子为载体的催化剂、负载多元金属催化剂以及负载金型催化剂的研究及应用情况也进行了总结和评述。     

Enantioselective Synthesis of Chromenes via a Palladium‐Catalyzed Asymmetric Redox‐Relay Heck Reaction

A palladium‐catalyzed asymmetric redox‐relay Heck reaction of 4H ‐chromenes and arylboronic acids has been successfully developed. The reaction proceeded in moderate to good yields with good to high enantioselectivities. The resulting product is an advanced intermediate of bio‐active compound BW683C.     

Biaryl Synthesis by Ring‐Opening Friedel–Crafts Arylation of 1,4‐Epoxy‐1,4‐dihydronaphthalenes Catalyzed by Iron Trichloride

Biaryl and heterobiaryl compounds are important frameworks across a range of fields including pharmaceutical and functional material chemistries. We have accomplished the efficient synthesis of various naphthalene‐linked arenes and heteroarenes as biaryls and heterobiaryls by the FeCl₃‐catalyzed Friedel‐Crafts reactions accompanied by the ring‐opening of the 1,4‐epoxy moiety of 1,4‐epoxy‐1,4‐dihydronaphthalenes. Especially, it is noteworthy that 1‐silylated substrates were regioselectively transformed to the 3‐aryl‐1‐silylnaphthalenes and the double Friedel–Crafts reactions using thiophene derivatives could directly produce the corresponding bis‐naphthlated thiophene derivatives.     

Asymmetric Decarboxylative 1,4‐Addition of Malonic Acid Half Thioesters to Vinyl Sulfones: Highly Enantioselective Synthesis of 3‐Monofluoromethyl‐3‐Arylpropanoic Esters

An asymmetric decarboxylative 1,4‐addition of malonic acid half thioesters (MAHTs) to 2‐aryl‐substituted vinyl sulfones has been developed, yielding adducts with excellent enantioselectivity (up to 97 % ee). In view of tuning pK_a values, a quinine‐based benzyl‐substituted thiourea was designed and demonstrated as the most efficient catalyst. The enantioselective synthesis of 3‐monofluorinated analogues of 3‐methyl indanone and (+)‐turmerone has been accomplished from decarboxylative 1,4‐addition adducts with satisfactory results.     

Catalytic Enantioselective Synthesis of 1,4‐Keto‐Alkenylboronate Esters and 1,4‐Dicarbonyls

A catalytic enantioselective method for the synthesis of 1,4‐keto‐alkenylboronate esters by a rhodium‐catalyzed conjugate addition pathway is disclosed. A variety of novel, bench‐stable alkenyl gem‐diboronate esters are synthesized. These easily accessible reagents react smoothly with a collection of cyclic α,β‐unsaturated ketones, generating a new C?C bond and stereocenter. Products are isolated in up to 99 % yield with greater than 20:1 E/Z and greater than 99:1 e.r. Mechanistic studies show the site‐selectivity of transmetalation and reactivity is ligand dependent. The utility of the approach is highlighted by gram‐scale synthesis of enantioenriched cyclic 1,4‐diketones, and stereoselective transformations of the products by hydrogenation, allylation, and isomerization.     

Enantioselective Synthesis of Tetrahydropyrano[3,4‐b]indoles: Palladium(II)‐Catalyzed Aminopalladation/1,4‐Addition Sequence

A novel palladium(II)‐catalyzed cyclization of aniline‐tethered alkynyl cyclohexadienones is reported. This reaction offers an atom‐economical and redox‐neutral access to various cyclohexenone‐fused tetrahydropyrano[3,4‐b ]indoles with high yield and excellent enantioselectivity. Remarkably, this work represents the first example on a transition‐metal‐catalyzed asymmetric intramolecular aminopalladation/1,4 addition sequence.     

Palladium‐Catalyzed Asymmetric Synthesis of Silicon‐Stereogenic 5,10‐Dihydrophenazasilines via Enantioselective 1,5‐Palladium Migration

A palladium‐catalyzed asymmetric synthesis of silicon‐stereogenic 5,10‐dihydrophenazasilines was developed that proceeds via an unprecedented enantioselective 1,5‐palladium migration. High enantioselectivity was achieved by employing 4,4′‐bis(trimethylsilyl) (R )‐Binap as the chiral ligand, and a series of mechanistic investigations were carried out to probe the catalytic cycle of this process.     

Radical Cyclization/ipso‐1,4‐Aryl Migration Cascade: Asymmetric Synthesis of 3,3‐Difluoro‐2‐propanoylbicyclo[3.3.0]octanes

A novel method for the asymmetric synthesis of 3,3‐difluoro‐2‐propanoylbicyclo‐[3.3.0]octanes involves an unprecedented intramolecular radical cyclization/ipso‐1,4‐aryl migration cascade.     

Synthesis of α‐Stereogenic Amides and Ketones by Enantioselective Conjugate Addition of 1,4‐Dicarbonyl But‐2‐enes

Constructing α‐stereogenic amides and ketones : The highly regioselective and enantioselective conjugate addition of 1,3‐dicarbonyl compounds to 1,4‐dicarbonyl but‐2‐enes has been developed with the chiral bicyclic guanidine as catalyst (ee values up to 97 %; see scheme).

     

Divergent Synthesis of CF3‐Substituted Allenyl Nitriles by Ligand‐Controlled Radical 1,2‐ and 1,4‐Addition to 1,3‐Enynes

A ligand‐controlled system that enables regioselective trifluoromethylcyanation of 1,3‐enynes has been identified, which provides access to a variety of CF₃‐containing tri‐ and tetrasubstituted allenyl nitriles. We disclose that the involved propargylic radicals can be selectively trapped by (Box)Cu^II cyanide, while the tautomerized allenyl radicals are trapped by (phen)Cu^II cyanide (Box= bisoxazoline, phen=phenanthroline). In addition, the reaction features broad substrate scope and excellent functional group compatibility. Moreover, this protocol represents a novel regioselectivity‐tunable functionalization of 1,3‐enynes via radicals, which we believe will have great implications for the development of catalytic systems for selectivity control in radical and organometallic chemistry.     

Rhodium/Chiral Diene‐Catalyzed Asymmetric 1,4‐Addition of Arylboronic Acids to Chromones: A Highly Enantioselective Pathway for Accessing Chiral Flavanones

Chromone has been noted to be one of the most challenging substrates in the asymmetric 1,4‐addition of α,β‐unsaturated carbonyl compounds. By employing the rhodium complex associated with a chiral diene ligand, (R,R)‐Ph‐bod*, the 1,4‐addition of a variety of arylboronic acids was realized to give high yields of the corresponding flavanones with excellent enantioselectivities (≥97 % ee, 99 % ee for most substrates). Ring‐opening side products, which would lead to erosion of product enantioselectivity, were not observed under the stated reaction conditions.