A Study on the Regioselectivity of the Cyclization Reaction of 5－Amino－1， 2， 4－triazole with Asym－l， 3－dicarbonyl Compound

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Polymerization of 1,3-Butadiene with Catalysts Based on Cobalt Dichloride Complexes with Aminophosphines: Switching the Regioselectivity by Varying the MAO/Co Molar Ratio

Several novel cobalt dichloride complexes with amino-phosphine bidentate ligands were synthesized and characterized.For some of them single crystals were obtained and their molecular structure was determined by X-ray diffraction method.All the complexes were then used in combination with MAO for the polymerization of 1,3-butadiene,obtaining polymers with different structures(i.e.,predominantly 1,2 or cis-1,4)mainly depending on the type of ligand and on the MAO/Co molar ratio.The behavior of these novel catalysts was compared with that exhibited,in the polymerization of the same monomer,by the systems CoCl_(2)(PR3)2-MAO and CoCl_(2)(PRPh2)2-MAO(R=alkyl or cycloalkyl group),and by the systems based on cobalt dichloride complexes with various bi-and tridentate ligands(e.g.,diphosphines,bis-imines,pyridyl-imines,bis-iminopyridines).The comparison between the different systems allowed us to make some clarity about the actual and effective role played by the various types of ligands in the polymerization of conjugated dienes with catalytic systems CoCl_(2)(L)-MAO,in which L=mono-,bi-,or tri-dentate ligand.

From Reactivity and Regioselectivity to Stereoselectivity: An Odyssey of Designing PIP Amine and Related Directing Groups for C-H Activation

What is the most favorite and original chemistry developed in your research group? Developing PIP amine for regio-and enantioselective methylene C-H activation. How do you get into this specific field? Could you please share some experiences with our readers?

Switchable regioselectivity in amine-catalysed asymmetric cycloadditions

Subject Code:B02 With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Prof.Chen Yingchun(陈应春)from Sichuan University and Dr.Ouyang Qin(欧阳勤)from the Third Military Medical University demonstrates switchable regioselective[6+2]。

Structure-guided manipulation of the regioselectivity of the cyclosporine A hydroxylase CYP-sb21 from Sebekia benihana

The cytochrome P450 enzyme CYP-sb21 from the rare actinomycete Sebekia benihana is capable of hydroxylating the immunosuppressive drug molecule cyclosporine A(CsA)primarily at the 4th N-methyl leucine(MeLeu4),giving rise toγ-hydroxy-N-methyl-L-Leu4-CsA(CsA-4-OH).This oxidative modification of CsA leads to dramatically reduced immunosuppressive activity while retaining the hair growth-promoting side-effect,thus demonstrating great application potential in both pharmaceutical and cosmetic industries.However,this P450 enzyme also hydroxylates CsA at the unwanted position of the 9th N-methyl leucine(MeLeu9),indicating that the regioselectivity needs to be improved for the development of CsA-4-OH into a commercial hair growth stimulator.Herein,we report the crystal structure of CYP-sb21 in its substrate-free form at 1.85Å.Together with sequence and 3D structure comparisons,Autodock-based substrate docking,molecular dynamics(MD)simulation,and site-directed mutagenesis,we identified a number of key residues including R294,E264,and M179 that can improve catalytic efficiency or change the regioselectivity of CYP-sb21 towards CsA,setting the stage for better enzymatic preparation of CsA-4-OH.This study also provides new insights into the substrate recognition and binding mechanism of P450 enzymes that accommodate bulky substrates.

Trifluoromethyl Radical Addition versus Radical Trifluoromethylation:Reversed Regioselectivity in Carbotrifluoromethylation of Alkenes

Professor Chaozhong Li's research group has long been interested in radicals in organic synthesis. They have developed a series of silver-catalyzed radical fluorination reactions since the year 2012.[1] In 2015, the research group joined the Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. I joined the Li group in the same year.

Post-spin crossing dynamics determine the regioselectivity in open-shell singlet biradical recombination

Radical recombination is among the fastest reactions in organic chemistry.Achieving high levels of selectivity in this type of reaction is rather challenging.In a recent report on visible-light-induced dearo-mative cycloaddition of pyrrole-tethered vinylcyclopropanes,extraordinary regioselectivity was observed during the intramolecular open-shell singlet biradical recombination step.

Regioselective enzymatic acylation of troxerutin in nonaqueous medium

A series of monosubstituted troxerutin esters have been synthesized by enzyme-catalyzed regioselective acylation of troxerutin in nonaqueous medium.Using divinyl dicarboxylates(CH_2=CH-OOC-(CH_2)_n-COO-CH=CH_2,n = 2,3,4,7,8,11) featuring different chain length as acyl donors and alkaline protease from Bacillus subtilis as catalyst,troxerutin was regioselective acylated at B' ethoxyl group.The results indicated that the regioselectivity of the enzyme-catalyzed acylation was not affected by the chain lengt...

Regioselective synthesis and anti-HIV activity of the novel 2- and 4-substituted pyrazolo[4,5-e] [ 1,2,4]thiadiazines

The new regioisomer 7-methyl-pyrazolo[4,5-e][1,2,4]thiadiazine nucleus (5) was synthesized, and its novel mono-N2- or N4-substituted pyrazolo[4,5-e][1,2,4]thiadiazines (6, 7) were regioselectively prepared by deprotonation of N2 or/and N4 atoms with different molar ratio of NaH and alkyl halides. Anti-HIV-1 screening tests showed some compounds to be potent as HIV-1 non-nucleoside reverse transcriptase inhibitors (HIV-1 NNRTIs).

Zinc Chloride Catalyzed Regioselective Nitration of Aromatic Hydrocarbons Using Tetrachlorosilane-Sodium Nitrate Homogeneous System

The development of a new silane reagent derived from tetrachlorosilane (TCS) was applied in the present work. TCS-sodium nitrate (NaNO3) binary reagent and zinc chloride (ZnCl2) were reported here as a homogeneous nitrating system. The later was used for the efficient mono nitration, in most cases, with high para-regioselectivity. The nitration proceeded smoothly under mild condition, fairly clean and in good yields. This readily available and inexpensive system is superior to other methods by avoidance of the use of corrosive nitrating reagents and therefore considered to be convenient in terms of risk reduction, economic advantages and environment protection. The present protocol was convenient and applicable to a variety of aromatic hydrocarbons and could be amenable to high throughput synthesis of combinatorial libraries for potential drug development, which needs to be studied as part of future investigations.

SYNTHESIS AND CATALYTIC BEHAVIOR OF POLYSILOXANESUPPORTED FULLERENE PLATINUM OR RHODIUM COMPLEXES

Two polysiloxanes with pendant fullerene moieties and their platinum or rhodium complexes havebeen prepared from C60 via amination with ω-decenylamine, followed by hydrosilylation with triethoxysilaneand immobilization on fumed silica or by hydrosilylation with methyldichlorosilane and polycondensationwith polydimethylsiloxanol, and then by reacting them with potassium chloroplatinite or rhodium chloride inacetone respectively under argon atmosphere. It was found that the four noble metal complexes are effectivecatalysts for the hydrosilylation of olefins with triethoxysilane. The regioselcctivity of platinum complexesfor styrene increases remarkably by introducing C60 moiety. Factors influencing catalytic activity and themechanism have been investigated.

Synthesis of 1,7-Bis(4-hydroxyphenyl)-3-hydroxy-1,3-heptadien-5-one

A facile synthesis of the analog of curcumin. 1,7-bis (4-hydroxyphenyl)-3-hydroxy-1,3-heptadien-5-one 1was achieved. The key step was completed through the regioselectivecondensation of ketone 5 and acyl chloride 7.

Regioisomeric Polymer Semiconductors Based on Cyano-Functionalized Dialkoxybithiophenes:Structure-Property Relationship and Photovoltaic Performance

Cyano substitution is vital to the molecular design of polymer semiconductors toward highly efficient organic solar cells.However,how regioselectivity impacts relevant optoelectronic properties in cyano-substituted bithiophene systems remain poorly understood.Three regioisomeric cyano-functionalized dialkoxybithiophenes BT_(HH),BT_(HT),and BT_(TT) with headto-head,head-to-tail,and tail-to-tail linkage,respectively,were synthesized and characterized in this work.The resulting polymer semiconductors(PBDTBTs)based on these building blocks were prepared accordingly.The regiochemistry and property relationships of PBDTBTs were investigated in detail.The BTHH moiety has a higher torsional barrier than the analogs BT_(HT) and BT_(TT),and the regiochemistry of dialkoxybithiophenes leads to fine modulation in the optoelectronic properties of these polymers,such as optical absorption,band gap,and energy levels of frontier molecular orbitals.Organic field-effect transistors based on PBDTBT_(HH) had higher hole mobility(4.4×10^(-3) cm^(2)/(V·s))than those(ca.10^(-4) cm^(2)/(V·s))of the other two polymer analogs.Significantly different short-circuit current densities and fill factors were obtained in polymer solar cells using PBDTBTs as the electron donors.Such difference was probed in greater detail by performing space-charge-limited current mobility,thin-film morphology,and transient photocurrent/photovoltage characterizations.The findings highlight that the BTHH unit is a promising building block for the construction of polymer donors for highperformance organic photovoltaic cells.

Oxidative coupling polymerization of p-alkoxyphenols with Mn(acac)2-ethylenediamine catalysts

The oxidative coupling polymerization of p alkoxyphenols with Mn(acac)2ethylenediamine catalysts was carried out. The polymerization of pmethoxyphenol with the manganese(II) acetylacetonate [Mn(acac)2]N,N’diethylethylene diamine catalyst in CH2Cl2 at room temperature under an O2 atmosphere afforded a polymer, which mainly consists of the mphenylene unit, whereas the polymer obtained with Mn(acac)2 was rich in the oxyphenylene structure. The polymer yield and regioselectivity were significantly affected by the monomer and catalyst structures. The former catalyst system was also used for the coupling reaction of 2methoxy 4methylphenol. The corresponding carboncar bon coupling product was isolated with a regioselectivity of 95%.

Pd-Catalyzed Microwave Irradiated Regioselective Aroylation Reaction of Crotyl- and Allyltrifluoroborates

An interesting regioselectivity is observed when the mixture of potassium crotyltrifluoroborate (1a) and aroyl chlorides having electron-deficient and electron-rich groups is microwaved in the presence of palladium-catalyst. In the case of electron withdrawing group with phenyl ring of aroyl chlorides, isomerized α,β-unsaturated compound 3 is the product whereas electron donating group with phenyl ring of aroyl chlorides furnishes α-adduct 4. Similar aroylation reaction is also established for potassium allyltrifluoroborate (1b). In this case, regioselectivity is unaffected with changing electron-rich or electron-deficient groups in phenyl ring of the aroyl chlorides. Reactions proceed with, essentially in same rate, affording the corresponding aryl propenyl ketones (crotonophenones) 5 in good to high yields.

Regio-and Stereo-selective Reductions of Steroidal 4-en-3,6-dione

The different regioselective and stereoselective products were obtained by the reduction of stigmast-4,22-dien-3,6-dione with NaBH4-CH3OH when different kinds of metal ions was added to the reaction.

Zn(NO_3)_2·6H_2O/2,4,6-trichloro-1,3,5-triazine(TCT) a mild and selective system for nitration of phenols

Certain phenols and naphthols were nitrated regioselectively with Zn(NO_3)_2·6H_2O/TCT in acetonitrile as solvent at room temperature and short reaction time in good yields.The reaction condition was mild.TCT is a cheap and commercially available reagent.It performed as an acid catalyst in this transformation.

An efficient chemo-and regioselective three-component synthesis of pyridazinones and phthalazinones using activated KSF

The first three-component and regioselective synthesis of pyridazinones and phthalazinones from arenes,anhydrides and ArNHNH2 in the presence of efficient recyclable heterogeneous catalyst,montmorillonite-KSF,in high yield and short reaction time is reported.

The Influence of Nitrate Salts and Complex Metal Ion to Regio-Selective Synthesis of 2-Nitro-5,10,15,20-Tetra- (4-Methoxyphenyl)Porphyrinato Metal

A series of 2\|nitro\|5,10,15,20\|tetra(4\|methoxyphenyl) porphyrinato metals were regioselectively synthesized with nitrate salts as nitrating reagent in acetic acid/acetic anhydride for preparation of 2\|substituted porphyrin. The influence of nitrate salts and complex metal ion to the reaction were investigated. The extent of 2\|nitration increased with the electronegativity of the central metal. When Cu(NO 3 ) 2 · 3H 2O was used as nitrating reagent, almost quantitative yields of 2\|nitro porphyrin were obtained in the case of Cu(Ⅱ) or Ni(Ⅱ) chelates, while Zn(Ⅱ) or Mn(Ⅲ) chelates gave 50% and 30% yields respectively. If Zn(NO 3 ) 2 ·10H 2 O was used as nitrating agent, no product was found for Cu(Ⅱ) or Ni(Ⅱ) chelates, 12% was found for Zn(Ⅱ) chelates. The other metal ion and nitrate salts were also found in quite different influence.