The Solvent Effect on the Chemoselectivity of Palladium-catalyzed Oligomerization of 3,3-Dimethyl-1-butyne

The chemoselectivities of PdCl2 and CuCl2-catalyzed oligomerization of 3, 3-dimethyl-butyne: 1, 3, 5-tri-tert-butylbenzene, 2, 2, 7, 7-tetramethyl-3, 6-dichloro-3, 5-octadiene and 2, 2, 7, 7- tetramethyl-3, 5-octadiyne were obtained, respectively, by regulating the polarity of the solvent.

New observation on a class of old reactions:Chemoselectivity for the solvent-free reaction of aromatic aldehydes with alkylketones catalyzed by a double-component inorganic base system

Solvent-free reactions of aromatic aldehydes with three representative ketones,including acetophenone,acetone and cyclohexanone,have been examined under the catalysis of a low-cost inorganic base system consisting of NaOH and K2CO3.It was found that the chemoselectivity of the reactions is in close relationship with the composition of the reactants and the doublecomponent catalyst.Under the optimized experimental conditions,1,2,3,4,5-pentasubstituted cyclohexanols,α,β-unsaturated ketones and Claisen-Schmidt bicondensation products were obtained in high yields.Two Kostanecki's triketones were separated,The composition and structure were affirmed by X-ray crystallographic analysis.

Lewis Base Catalyzed Selenofunctionalization of Alkynes with Acid-Controlled Divergent Chemoselectivity

Lewis base catalyzed and Brønsted acid controlled chemodivergent electrophilic selenofunctionalizations of alkynes were developed for the first time.Various selenium-containing tetrasubstituted alkenes were readily obtained in moderate to excellent yields with complete E/Z selectivities.As the substrates were 1-ethynyl naphthol derivatives,linear selenium-containing tetrasubstituted alkenes were produced via intermolecular oxygen nucleophilic attack in the absence of acid additive;in contrast,cyclic selenium-containing tetrasubstituted alkenes were generated through intramolecular carbon nucleophilic capture with the addition of Brønsted acid.

Ferrous methanesulfonate as an efficient and recyclable catalyst for chemoselective synthesis of 1,1-diacetate from aldehydes

Ferrous methanesulfonate catalysing the conversion of aromatic, heteroaromatic, unsaturated, and aliphatic aldehydes to 1,1- diacetates at room temperature under solvent-free condition has been developed. The catalytic activity of seventeen metal methanesulfonates was compared under the same condition, ferrous methanesufonate proved to be the best. It can be easily recovered and reused for several times without distinct deterioration in catalytic activity. During the competitive protection between a ketone and an aldehyde group with Ac20, 1,1-diacetate formed exclusively with the aldehyde group. 2009 Min Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Ultrasound-assisted Highly Efficient Reduction of Nitroarenes to Corresponding N-Arylhydroxylamines

A convenient, environmentally benign, and highly efficient protocol for the preparation of N-arylhydroxylamines from the corresponding nitroarenes in a Zn/HCOONH4/CH3CN system under ultrasound is described The advantages of the present method include high chemoselectivity, simple and practical work-up procedure and high yield.

Esterification and Chemoselective Synthesis of R-Tetrahydrothiazo-2-thione-4-carboxylic Esters Catalyzed by TiCl_4

A series of esters of R-tetrahydrothiazo-2-thione-4-carboxylic acid [ R-TTCA ] was synthesized by direct esterifica- tion of R-TTCA with alcohols（CH3OH, C2H5OH, n-C3HTOH, i-C3HTOH, n-C4H9OH, sec-C4H9OH） in the presence of TiCl4 as the catalyst at room temperature without using any other solvent or dehydrant in high yields, 91.6%-99.1% for primary alcohols and 55%- 80% for secondary alcohols. The catalyst has a strong chemoselec-tive activity for the esterification of primary alcohols with R-TTCA in the presence of secondary alcohols. Owing to high yield, high chemoselectivity, and mild conditions used, this is an efficient method for the esterification of prima-ry alcohols with R-TTCA.

Esterification and Selective Esterification in the Presence of TiCl_4

A series of carboxylic acids was esterified to the corresponding esters with TICl4 as catalyst at room temperature, in high yields. This catalyst was highly effective for the selective esterification of primary alcohols with carboxylic acids, in the presence of secondary alcohols, and for the selective esterification of saturated acid with alcohol in the presence of conjugated acid or aromatic acid. On account of the high yield, high chemoselectivity, mild condition, and being free of other dehydrants, this is an efficient method.

无溶剂条件下N-磺酸琥珀酰亚胺催化乙酰化反应(英文)

A small amount of succinimide-N-sulfonic acid efficiently catalyzed the acetylation of a variety alcohols, phenols, thiols, amines and aldehydes with acetic anhydride at room temperature under solvent free conditions. This catalyst has the advantages of excellent yields and short reaction times and the reaction can be carried out on a large scale, which makes it potentially useful for industrial applications.

Chemoselective Bromodecarboxylation ofα-Carboxy-α-cinnamoyl Ketene Cyclic Dithioacetals

α-Oxoketene dithioacetals（ compound 1 ） are versatile synthons for organic synthesis due to their specially structural characteristic, that is, the masked ketene is conjugated with the convertible carbonyl in their molecules. Although there have been numerous reports covering the reactions in which they have been taken as 1,3-electrophiles, the reaction at the α-carbon atom of α-oxoketene dithioacetals has seldom been investigated. Junjappa and co-workers found the α- bromination of compound 2 in the presence of NBS led to α-aroyl-α-bromo ketenedithioacetals. However, the flexibility of the functional groups at the α-carbon atom of compound 2 are still limited.

Henry Reaction in Aqueous Media: Chemoselective Addition of Aldehydes

The chemoselective addition of aldehydes in aquoues medium was obtained under mild condition using improved Henry reaction.

Chemoselective synthesis of δ-lactones via benzyl radical cyclization utilizing K_2S_2O_8-CuCl_2

Direct chemoselective oxidation of δ-lactones via highly stable benzyl radical cyclization is reported. The one-pot conversion of premade substituted 5-aryl pentanoic acid and 8-benzyl-1-naphthoic acid in the presence of K2S2Os--CuCl2 results to the δ-lactones in moderate to good yields. The advantages of this methodology is using water as a solvent and utilizing available starting materials.

A Facile Procedure for Conjugate Addition of Amines to Electron Deficient Alkenes with Metal Oxide as Catalyst

A novel efficient procedure has been developed for the conjugate addition of amines to electron deficient alkenes. A series of metal oxides was synthesized for catalyzing the conjugate addition of amines and alkenes. After optimizing the reaction conditions, SrO was chosen as the most efficient catalyst for the reactions. The results show that the catalyst is very efficient for the conjugate addition of amines to electron deficient alkenes with the excellent yields in several minutes. Operational simplicity, without need of any solvent, low cost of the catalyst used, high yields, reusability, excellent chemoselectivity and applicability to large-scale reactions are the key features of this methodology.

Chemoselective Catalytic Hydrogenation of Nitroarenes Using MOF-Derived Graphitic Carbon Layers Encapsulated Ni Catalysts

Replacement of precious noble metal catalysts with cost-effective,non-noble heterogeneous catalysts for chemoselective hydrogenation of nitroarenes holds tremendous promise for the clean synthesis of nitrogen-containing chemicals.Graphitic carbon layers encapsulated Ni catalysts(Ni@CN)are generated by a facile,scalable and straightforward strategy via the pyrolysis of 2,5-pyridinedicarboxylic acid coordinated Ni-MOF acting as the precursor.Physicochemical properties of the Ni@CN catalysts have been investigated by X-ray diffraction,scanning electron microscopy,transmission electron microscopy,elemental analysis and N2 adsorption-desorption analysis.The Ni@CN catalysts were found to be highly efficient in the chemoselective hydrogenation of various nitroarenes with other functional groups towards corresponding anilines under mild reaction conditions(85℃,1.0 MPa of H2 pressure).Based on the results of controlled tests,the catalytic activity can be attributed to the Ni NPs,while the presence of graphitic carbon layers favors the preferential adsorption of the nitro groups.The recyclability and anti-sulfur poisoning capability of Ni@CN were also investigated.

6-Azido-Galactosyl Imidate as a Building Block for Preparation of 1-(4-Aminobutyl)-, Di-, Tri- and Tetra-Saccharides

6-azidogalactosyl imidate has been used as a donor to generate 1-(4-aminobutyl)-6-aminogalactose, 6-aminothiotolyl- glycosides of disaccharide, trisaccharide and tetrasaccharide that incorporates 6-azido group and 1-(4-tolyl)thio group. Trisaccharide and tetrasaccharide were obtained from lactosyl-based acceptor. The anomeric 1-(4-tolyl)thio group could be used to conjugate with sphingosine analogs to provide the alpha-Gal Sph analogs for library extension from the azido group.

Chemoselective Reduction of Fenofibric Acid to Alcohol in the Presence of Ketone by Mixed Anhydride and Sodium Borohydride

A highly efficient and facile protocol for the selective reduction of carboxylic acid of Fenofibric acid to corresponding alcohol was developed. The selective reduction was carried out by activation of carboxylic acid by mixed anhydride followed by the reaction of sodium borohydride in presence of methanol. This is the first example of chemoselective reduction of carboxylic acid to alcohol in presence of a ketone without any external catalyst or ligand in a single step. The reaction offers wide applicability for the selective carboxylic group reduction methodology. The chemoselective reduction was demonstrated by the reduction of Fenofibric acid, an active metabolite of the drug Fenofibrate, to corresponding alcohol in excellent selectivity, yield, and purity.

Chemoselective and Living/Controlled Polymerization of Alkenyl Methacrylates by the Phosphonium Ylide/Organoaluminum Lewis Pairs

Chemoselective,living/controlled polymerizations of allyl methacrylate(AMA) and vinyl methacrylate(VMA) with/without methyl methacrylate(MMA) by using the phosphonium ylide/organoaluminum based Lewis pairs(LPs) have been realized.The P-ylide-2/AIMe(BHT)_(2)(Pylide-2=Ph_(3)P=CHMe and BHT=2,6-iBu_(2)-4-MeC_(6)H_(2)O) was demonstrated to be superior by which homopolymers PAMAs(M_(n)=27.6-111.5kg/mol and ■=1.14-1.25) and PVMAs(M_(n)=28.4-78.4 kg/mol and ■=1.12-1.18) and block copolymers PMMA-b-PAMA,PAMA-b-PVMA,PAMA-bPMMA,PMMA-b-PAMA-b-PMMA,PAMA-b-PMMA-b-PAMA,and PAMA-b-PVMA-b-PAMA were synthesized.In the polymerizations,all of the monomers were reacted by the conjugated ester vinyl groups leaving intactly the nonconjugated acryloxy groups.The pendant acryloxy groups attached to the main chain enable further to post-functionalization by the AIBN-induced radical "thiol-ene" reaction using PhCH_(2)SH.The thiolether side group-containing polymers PAMA-SCH_(2)Ph and PAMA-SCH_(2)Ph-b-PMMA-b-PAMA-SCH_(2)Ph were thus prepared.

Chemoselective labeling-based spermatozoa glycan imaging reveals abnormal glycosylation in oligoasthenotspermia

Spermatogenesis, maturation, capacitation and fertilization are precisely regulated by glycosylation. However, the relationship between altered glycosylation patterns and the onset and development of reproductive disorders is unclear, mainly limited by the lack of in situ imaging techniques for spermatozoa glycosylation. We developed an efficient and highly specific spermatozoa glycan imaging technique based on the robust chemoselective labeling of sialic acid(Sia) and N-acetyl-D-galactosamine(Gal/GalNAc). We further proposed a “tandem glycan chemoselective labeling” strategy to achieve simultaneous imaging of two types of glycans on spermatozoa. We applied the developed method to the spermatozoa from oligozoospermic patients and diabetic mice and found that these spermatozoa showed higher levels of Sia and Gal/Gal NAc expression than the normal groups. Moreover, spermatozoa from diabetic mice showed a severe decrease in number, viability, and forward motility, suggesting that in vivo glucose metabolism disorders may lead to an elevated level of spermatozoa glycosylation and have a correlation with the development of oligoasthenotspermia. Our work provides a research tool to reveal the relationship between glycosylation modification and spermatozoa quality, and a promising clue for the development of glycan-based reproductive markers.

Carbon dots-incorporated CuSeO_(3)rationally regulates activity and selectivity of the hydrogen species via light-converted electrons

The chemoselective hydrogenation of structurally diverse nitroaromatics is a challenging process.Generally,catalyst activity tends to decrease when excellent selectivity is guaranteed.We here present a novel photocatalyst combining amino-functionalized carbon dots(N-CDs)with copper selenite nanoparticles(N-CDs@CuSeO_(3))for simultaneously improving selectivity and activity.Under visible light irradiation,the prepared N-CDs@CuSeO_(3)exhibits 100%catalytic selectivity for the formation of 4-aminostyrene at full conversion of 4-nitrostyrene in aqueous solvent within a few minutes.Such excellent photocatalytic performance is mainly attributed to the precise control of the hydrogen species released from the ammonia borane by means of light-converted electrons upon N-CDs@CuSeO_(3).Besides,the defect states at the interface of N-CDs and CuSeO_(3)enable holes to be trapped for promoting separation and transfer of photogenerated charges,allowing more hydrogen species to participate in catalytic reaction.

Fe(III)-Catalyzed Aerobic Oxidation of 1,4-Diols

Comprehensive Summary Aerobic oxidation has been catching more and more attention because of its atom economy and environmental friendliness.Oxidation of diols is a challenge due to various oxidative products.Thus,highly selective aerobic oxidation affording specific products is of current interest.In this work,a combination of Fe(NO_(3))_(3)·9H_(2)O/TEMPO/KCl catalysis has been identified as an efficient recipe for the aerobic oxidation of 1,4-diols affordingγ-butyrolactones under mild conditions.The reaction exhibits decent chemo-and regioselectivity of symmetrical and unsymmetrical 1,4-diols.The optically activeγ-lactones may also be prepared from optically active 1,4-diols without erosion of the ee via this method.Furthermore,this approach was successfully applied to synthesize NBP,a commercial drug.

Ni-catalyzed ligand-controlled divergent and selective synthesis

Scaffold diversity is a key feature of a compound library and plays a pivotal role in its success in biological screening.Therefore,it is highly desirable to develop efficient strategies to rapidly construct structurally distinct and diverse“privileged”molecular scaffolds,thereby giving rise to compound libraries with selective and differing biological activities.This review covers recent efforts in this emerging field of Ni-catalyzed divergent and selective synthesis,and will focus on reactions using the same substrate to generate structurally diverse molecular scaffolds by varying the ligand backbone under otherwise almost identical reaction conditions.We hope that the field will be encouraged by the progress achieved,drawing attention to the design and development of new selective catalytic systems,and revealing new modes of catalytic transformation for broader synthetic applications.