Synthesis of 2-Arylbenzofuran: Confirmation of the Structure of Gnetifolin A

GnethelinAu'asisolatedfromGnetumparvghlium(Warb.)C.Y.Chengb}'Lietal.'ItSstructUrextasproPosedpre\'iousl}'as2-(3.5allhydroxT4-methomphen}l)-3-methony-5-hydrox3-benLzofiiran(l).Aner9'nthesisofset1eralanalogsofStrUctUre(l),theStrUCtUrofGnetjfolinAseemstobenustakenanduasrerisedas2K3-5allhydrOny4-methomphenyl)4-methoxy-5-hvdrowtenzofuran(2).=Inordertoconfirmthisrer4ndmCtUranddevelopaversahlewtehcrouteforthe9-nthesisofGnetjfolinAandanalogs,2T-edSyl4-methoxy-5-hydrotwllZofuran(3)u'asselec…     

Chiral Synthesis of the Key Intermediate of Diterpenoids

(-)-Methyl(4R,5SloR)-l4-methoxyPodocmpa-8,ll,l3-triene-l9-oate(I)isthekeyintermediateforsynthesesofditerpenoidssuchaskaurenoicacid(3),kaur-l6-en-l9-ol(4),monoginol(5)('),aswellasC,,-diterpenealkaloidssuchasveachine(6),garryine(7)andatisine(8)(=).TheracemicsynthesisofthisintermediatewasdonebyK.Morietar'),butthechiralsynthesishasnotbeenreported.Herewepresentthechiralsynthesisofthiskeyintermediatefrom(R)-(+)-2-methyl-2-(2'-nitrovinyl)-5-vaierolactone(2).2wassynthesizedaccordingtoliterattirmeth…     

Syntheses and Characterization of Heterocyclic Compounds of Zirconium ( Ⅳ )

The Zr-H bond of zirconocene hydridochloride was heterolyzed at room temperature by five compounds containing nitrogen and hydroxyl group to give Cp(Q)2ZrCl(1) (Cp = cyclopentadienyl and Q = 8-quinolinoyl ) , Cp (Q-Me )2ZrCl (2) , Cp(5,7-Br2Q)2ZrCl(3), Cp2(2-pyridoyl)ZrCl(4) , and Cp(2-aminoethanoyl)2ZrCl(5), which were characterized by elemental analysis, IR, and 1H NMR spectroscopy. The molecular structure of 1 was confirmed by X-ray diffraction determination. The crystal of 1 crystallized monoclinically, space group P21/n a= 0.9004(2), b=1.3961(2), c = 1. 6056(2) nm, β=99. 48(1)°? V=1. 9906 nm3, Z = 4, and Dc=1. 582 g/cm3. The coordination polyhedron around the Zr atom can be described as a distorted octahedron. The Zr-N bonds of 0. 2364(3) and 0. 2377(4) nm suggest that they are coordination bonds. The two planar 8-quinolinoyl groups as bidentate ligands chelate with Zr atom, forming a dihedral angle of 108. 4(1)°?     

Influence of Aging Time on the Properties of Precursors of CuO／ZnO Catalysts for Methanol Synthesis

The aging process of pure copper precursors and copper-zinc binary precursors were studied by XRD, TG-DTG and TPR techniques. The catalytic activity and stability of CuO/ZnO were tested using fixed-bed flow reactor, and the physical properties of the catalysts and Cu species were characterized with N2 adsorption and N2O passivation method, respectively. For the Cu-Zn binary system prepared at the precipitating condition of pH=8.0 and temperature=80℃, the initial phase was a mixture of copper nitrate hydroxide Cu2(NO3)(OH)3, georgeite and hydrozincite Zn5(CO3)2(OH)6. By increasing the duration of its aging time, the phase of Cu2(NO3)(OH)2 first transited to georgeite, and then interdiffused into Zns(CO3)2(OH)6 and resulted in two new phases: rosasite (Cu,Zn)2CO3(OH)2 and aurichalcite (Zn,Cu)5(CO3)2(OH)6. The former phase was much easier to be formed than the latter one, while the latter phase was more responsible for the activity of methanol synthesis than the former one. It is found that the composition and structure of the precursors altered obviously after the colour transition point. The experimental results showed that methanol synthesis is a structure-sensitive catalytic reaction.     

The Preparation and Application of two New Types of Oxazaborolidines

Stereoselectivereductionoftheprochiralketonesisoneofthemostactivelystudiedareasinasymmetricsynthesis.Inthiscontext,oxazaborolidinecatalysedreductionhasemergedasoneofthemostprominentmethodology'.(is,Zs)-2-amino-l-(4-nitrophenyl)-propane-l,3-diolIisaby-productinthechloramphenicolmanufacture.Inthispaped,wereporttheresultsofthecatalyticasy-mmetricreductionofacetophenoneswithboraneinthepresenceofchiralligandart-singfrom1.Thepreparationofligand2isscheduledand3canbeproducedfrom12.The10%mol.of2or3rea…     

Syntheses and Structural Characterization of Dimethyltin Complexs of N-（3-Methoxysalicylidene）-α-amino Acid

Three new dimethyltin complexes of N-(3-methoxysalicylidene)-α-amino acid,(CH3)2Sn(3-CH3O-2-OC6H3CH=NCHRCOO)(R = H,1;CH3,2;(CH3)2CH,3),have been synthe-sized by treating dimethyltin dichloride with the potassium salt of the ligand and characterized by elemental analysis,IR and 1H NMR spectra.The crystal structure of [(CH3)2Sn(3-CH3O-2-OC6H3CH=NCH2COO)(CH3OH)]2 H2O(1a),formed from methanol solution of 1,has been deter-mined.The crystal belongs to the monoclinic system,space group C/2c with a = 20.636(3),b = 7.8854(9),c = 20.668(2) ,β= 113.265(2)°,V = 3089.7(6) 3,Z = 4,Dc = 1.707 g/cm3,= 1.675 mm-1,F(000) = 1592,R = 0.0301 and wR = 0.0841.In complex 1a,the tin atom is six-coordinate and possesses a distorted [SnC2NO3] octahedral geometry with the two methyl groups occupying the trans positions.The weak Sn O interactions and intermolecular hydrogen bonds connected the molecules into an infinite chain.     

Syntheses of a new type of chiral phosphines from glucose

Methyl 3-deoxy-3-(diphenylphosphino)-4,6-O-benzylidene-α-D-altropyranoside (1) and methyl 2-deoxy-2-(diphenylphosphino)-4,6-O-benzylidene-α-D-altropyranoside (2) were prepared from methyl 2,3-anhydro-4,6-O-benzylidene-O-D-mannopyranoside and methyl 2,3-anhydro-4,6-O-benzyl-idene-α-D-allopyranoside,respectively,via regioselective and stcreospecific ring-opening reactions in high yields.Compounds 1 and 2 were oxidized to give the corresponding phosphine oxides (3 and 4).     

Structure and magnetic properties of homobinuclear gadolinium (Ⅲ) complex of isonicotinoyl hydrazone

The crystal structure of [Gd2(μ-L)3(H2O)2].1.5(NO3).1.5 (OH)-5H2O (where L is an-ion of N, N'-Diisonicotinoyl-2-hydroxy-5-methyl-isophthalaIdehyde dihydrazone) has been determined by X-ray diffraction method. The complex crystallizes in the monoclinic system, space group P21/c with a=1.6654(3), b=1.6904(3), c=2.8039(6) nmβ=91.30(3)°, final R factor is 6.3%. The structrue consists of [Gd2(μ-L)3(H2O)2]3+ cation, one and a half nitrate and 1.5 hydroxyl anions and five water molecules. Within dinuclear cation, Gd(Ⅲ)-Gd(Ⅲ) is bridged by oxygen and nitrogen atoms of the three ligands, resulting in Gd...Gd distance of 0.36353(2) nm. Gd(Ⅲ) exhibits a distorted 1333 stack coordination environment. Magnetic susceptibility measurements in the temperature range 300-4 K revealed the occurrence of weak antiferromagnetic exchange interaction between two Gd(Ⅲ) ions with a J value of -0.22, and g of 1.93.     

Crystal structure and thermal decomposition mechanism of the supramolecular complex of barium chloride with inositol

The single crystal of [Ba(H2O)2(C6H12O6)2Cl2] was obtained based on the phase equilibrium results. Its structure was determined by X-ray crystallographic analysis. The crystals are monoclinic and in space group C2/c with a=1.901 7(2) nm, b = 0.682 13(8) nm, c = 0.162 60(2) nm,β=96.593(2)°and V= 2.095 3(4) nm3, Z= 4, DC=1.917 g·cm-3. In its solid state, this supramolecular complex is a three-dimensional network with double layers connected by hydrogen bondings. The molecule structure of [Ba(H2O)2(C6H12O6)2Cl2] has a central barium ion that is coordinated to two water molecules, two chlorides, and four hydroxyls from the two inosi-tols. Losing the coordinating water is controlled by random nucleation and growth mechanism (n = 2/3) and 3-dimensional diffusion mechanism (n=2).     

Study on the Synthesis of La（3）-doped Nano-TiO_2 and Photocatalytic Degradation of Methyl Orange

In this paper,La(3)-doped Nano-TiO2(La(3)-TiO2) was synthesized via hydrothermal process.Structure and optical properties of the synthesized samples were characterized via XRD,FT-IR,DRS,etc.The results showed that the phase transformation of TiO2 from anatase to rutile was effectively prevented by La(3)-doping,which improved the thermal stability of anatase,and also suppressed particle aggregation and grain growth of TiO2.The formation of Ti-O-La bond promoted UV absorption intensity of TiO2,and provoked red shift of absorbed light.And the spectra response range of TiO2 was extended significantly to visible light by La(3)-doping,then photocatalytic performance was improved effectively.Compared with pure nano-TiO2,the performance of La(3)-TiO2 which photocatalyticly degraded methyl orange was increased significantly.     

（R）-螺[4，5]癸-2，7-二酮的合成

从环己烯酮出发，经手性催化的Michael加成反应，Wolff重排反应延长碳链， 再利用重氮化合物的C-H插入反应，以8步反应28．5％的总收率合成了手性β，β '-螺二酮．在合成路线中手性中心的构型保持不变．在最后的检测中未发现另一对 映体，开始产生的手性中心在合成过程没有消旋化。     

Dirhodium tetracarboxylate derived from adamantylglycine as a chiral catalyst for carbenoid reactions

[reaction: see text] The dirhodium tetracarboxylate, Rh2(S-PTAD)4, derived from adamantylglycine, is a very effective chiral catalyst for carbenoid reactions. High asymmetric induction was obtained in Rh2(S-PTAD)4-catalyzed intramolecular C-H insertion (94% ee), intermolecular cyclopropanation (99% ee), and intermolecular C-H insertion (92% ee).     

Regio- and diastereocontrolled C-H insertion of chiral gamma- and delta-lactam diazoacetates. Application to the asymmetric synthesis of (8S,8aS)-8-hydroxyindolizidine

gamma- and delta-Lactam diazoacetates undergo efficient intramolecular C-H insertion catalyzed by Rh2(MPPIM)4 with excellent regioselectivity and cis-diastereoselectivity to provide synthetically useful bicyclic lactam lactones.     

Total synthesis of (+)-przewalskin B

An efficient strategy for the total synthesis of (+)-przewalskin B is reported. The key steps feature an intermolecular S(N)2' substitution of iodoallylic phosphate with organocupper reagent, a diastereoselective organocatalytic aldol cyclization, as well as a Rh(2)(OAc)(4)-mediated intramolecular carbene insertion to the tertiary C-H bond.     

Cycloaddition chemistry of 2-vinyl-substituted indoles and related heteroaromatic systems

[reaction: see text] The intramolecular Diels-Alder cycloaddition reaction (IMDAF) of several N-phenylsulfonylindolyl-substituted furanyl carbamates containing a tethered pi-bond on the indole ring were examined as an approach to the iboga alkaloid catharanthine. Only in the case where the tethered pi-bond contained two carbomethoxy groups did the [4 + 2]-cycloaddition occur. Push-pull dipoles generated from the Rh(II)-catalyzed reaction of diazo imides, on the other hand, undergo successful intramolecular 1,3-dipolar cycloaddition across both alkenyl and heteroaromatic pi-bonds to provide novel pentacyclic compounds in good yield and in a stereocontrolled fashion. The facility of the cycloaddition was found to be critically dependent on conformational factors in the transition state. Ligand substitution in the rhodium(II) catalyst markedly altered the product ratio between [3 + 2]-cycloaddition and intramolecular C-H insertion. The variation in reactivity reflects the difference in electrophilicity between the various rhodium carbenoid intermediates. Intramolecular C-H insertion is enhanced with the more electrophilic carbene generated using Rh(II) perfluorobutyrate.     

Rh(II) catalysed intramolecular C-H insertion of diazo substrates in water: a simple and efficient approach to catalyst reuse

Water is an efficient solvent for the Rh2(OAc)4 catalysed intramolecular C-H insertion of a range of diazo substrates without competitive water insertion. Due to the high solubility and stability of the catalyst in water, the catalyst can be efficiently reused.     

Vinyl diazophosphonates as precursors to quaternary substituted indolines and cyclopentenes

Vinyl diazophosphonates can be stereoselectively synthesized and, depending upon their substitution pattern, undergo intramolecular C-H insertion reactions or sulfonium ylide rearrangements when exposed to Rh(2)(OAc)(4).     

A Linear Free Energy Correlation Study of Rh(Ⅱ)-Mediated Carbenoid Intramolecular C-H Insertion

The reaction mechanism of Rh(Ⅱ)-mediated carbenoid intramolecular C-H insertion have been intensively investigated. The reaction has been observed to be affected by the electrophilicity of the Rh(Ⅱ)-carbene intermediate, the substituents on the carbon at which the C-H insertion occurs, and steric and conformational factors.¹ It has been well documented that the electronic property of the ligands of the Rh(Ⅱ) catalyst has marked influence over the electrophylicity of Rh(Ⅱ)-carbene intermediate. In addition, the α-substituent on the carbenoid carbon are expected to exert similar affect on the reactivity of Rh(Ⅱ)-carbene. According to the reaction mechanism proposed by Doyle, an electron-donating α-substituent decreases the electrophilicity of the Rh(Ⅱ)-carbene complex and causes the C-H insertion to occur with a later transition state,while an electron withdrawing α-substituent operates in the opposite way. However, this prediction is still lack of solid support by experimental data. Most of the studies on the electronic effects have so far been concentrated on electron-withdrawing α-substituent, such as ester or acetyl group. The α-substituent effect, although important, is generally subtle and may be readily overridden by other effects, such as steric and conformational effects. This makes it difficult to accurately evaluate the α-substituenteffect.     

Rh(II)-catalyzed intramolecular C-H insertion of diazo substrates in water: scope and limitations

Preferential Rh(II) carbenoid intramolecular C-H versus O-H insertion derived from alpha-diazo-acetamides can be achieved in water by using an appropriate combination of the catalyst and amide groups, which creates a larger hydrophobic environment around the reactive carbenoid center.     

Expanding the scope of C-H amination through catalyst design

Analysis of the mechanism for Rh-mediated C-H amination has led to the development of a remarkably effective dinuclear Rh catalyst derived from 1,3-benzenedipropionic acid. This unique complex, Rh2(esp)2, is capable of promoting both intra- and intermolecular C-H oxidation reactions, and in all cases is superior to Rh2(O2CtBu)4. For the first time, C-H insertion is described with urea and sulfamide substrates to give 1,2- and 1,3-diamine derivatives, respectively. In addition, intermolecular amination of benzylic and secondary C-H bonds is shown to proceed efficiently even under conditions in which the starting alkane is employed as the limiting reagent.