Visible light mediated metal-free oxidative aromatization of 1,3,5-trisubstituted pyrazolines

The visible light mediated oxidation of 1,3,5-trisubstituted pyrazolines under metal-free conditions was developed. Various substituted pyrazolines were oxidized to pyrazoles by irradiation with visible light/sunlight. A plausible mechanism was proposed for the light mediated oxidation proceeding via formation of intermediates with electron rich C-3 positions and electron deficient C-5 positions. Correlation between the electronic effect induced by the aryl substituents and the rate of oxidation was studied by UV–vis spectroscopy. This correlation study supported the proposed mechanism. Electron withdrawing substituents at the 3-phenyl group and electron releasing substituents at the 5-phenyl group enhanced the rate of oxidation; whereas, electron donating substituents at the 3-phenyl group and electron withdrawing substituents at the 5-phenyl group reduced the rate.     

Synthesis of unsymmetrical biaryl ureas from N-carbamoylimidazoles: kinetics and application

N-Carbamoylimidazoles dissociate in solution to yield imidazole and an isocyanate that may be reacted with another aryl amine to form an unsymmetrical biaryl urea. This paper investigates the reaction kinetics and the influence of electron withdrawing/donating substituents on the reaction of N-carbamoylimidazoles with aniline. The overall reaction mechanism involves two zwitterionic intermediates, formed during dissociation and upon reaction of the liberated isocyanate with aniline. The rate limiting step for the reaction is a base catalysed proton transfer from the second zwitterionic intermediate. Although electron withdrawing substituents on the aryl group hinder dissociation, they significantly increase reaction rates compared to compounds bearing electron donating substituents. The imidazole liberated upon dissociation catalyses the rate determining step so that reactions of dissociated N-carbamoylimidazoles proceed more rapidly than those involving only isocyanates. In addition, the imidazole eliminates the need for anhydrous reaction conditions. The N-carbamoylimidazole methodology was demonstrated by preparing sorafenib, a biaryl urea kinase inhibitor, in good yield and excellent purity.     

Computational studies on the electrocyclizations of 1-amino-1,3,5-hexatrienes

Electrocyclizations of 1,3,5-hexatrienes containing up to four electron-donating and/or electron withdrawing substituents have been studied computationally using the hybrid density functional, B3LYP. Electron donating substituents at positions C-1 and C-5 decrease activation barriers by 0.3 to 2.3 kcal/mol. Introducing of an electron-withdrawing group, CO(2)Me, at C-4 further decreases the activation energy by 7 kcal/mol. Electron-withdrawing groups (NO(2), SO(2)Ph and C=N(+)Me(2)) at C-2 have a profound effect of 17-25 kcal/mol on the activation energy.     

Substituent effect on redox potential of nitrido technetium complexes with Schiff base ligand: Theoretical calculations

Theoretical calculations based on the density functional theory (DFT) were performed to understand the effect of substituents on the molecular and electronic structures of technetium nitrido complexes with salen type Schiff base ligands. Optimized structures of these complexes are square pyramidal. The electron density on a Tc atom of the complex with electron withdrawing substituents is lower than that of the complex with electron donating substituents. The HOMO energy is lower in the complex with electron withdrawing substituents than that in the complex with electron donating substituents. The charge on Tc atoms is a good measure that reflects the redox potential of [TcN(L)] complex.     

取代基对α-氨基乙腈热解反应影响的研究

用MINDO/3方法洋细研究了取代基对α-氨基乙腈热消除反应的影响. 研究表明, 对于孤立分子的气相反应, 给电子基使活化势垒降低, 吸电子基使活化势垒上升; 而对OH~-催化下的反应, 给电子基和吸电子基均使活化势垒上升.     

Zinc oxide (ZnO) as a new, highly efficient, and reusable catalyst for acylation of alcohols, phenols and amines under solvent free conditions

Zinc oxide (ZnO) is a highly efficient catalyst for the acylation of a variety of alcohols, phenols and amines with acid chlorides or acid anhydrides under solvent free conditions. Primary, secondary, tertiary, allylic and benzylic alcohols, diols and phenols with electron donating or withdrawing substituents can be easily acylated in good to excellent yield.     

锡-铟促进和微波辐射辅助下醛和炔丙基溴的炔丙基化反应

A rapid and regioselective preparation of homopropargyl alcohols was reported. In the presence of SnCl2C6HsMe3NBr and microwave irradiation, the mixture of tin-indium and propargyl bromide reacted quickly with aldehydes in aqueous media to produce the homopropargyl alcohols exclusively in high yields. For benzaldehydes bearing different substituents, electronic effect of the substituents affected the reaction, the electron-withdrawing groups promoting the reaction and the electron-donating groups impeding the reaction. The reactions of benzaldehydes bearing an ortho substituent group on the phenyl ring with propargyl bromide may yield a mixture of regioisomers （homopropargyl and homoallenyl alcohols） or a single homoallenic alcohol due to the steric effect.     

A molecular orbital analysis of Cu(I)-catalysed cyclopropanation using diazoalkanes with CH3 and CF3 substituents

The mechanism of cyclopropanation catalysed by Cu(I) complexes has been investigated by calculation using a series of diazoalkanes containing inductive electron donating (methyl) and withdrawing (CF3) substituents and a range of metal fragments (Cu+, [(DAB)Cu]+, ClCu and (triflate)Cu). Copper-diazoalkane complexes exist as an equilibrium of C- and N-bonded isomers. Catalysis occurs through lowering of the activation energy for rate determining C-N bond cleavage of the C-bonded isomer; this is most marked for (triflate)Cu. Direct reaction of the copper-carbene complex occurs to yield stable cupracyclobutanes in all but one case. Associative substitution of the cupracyclobutane by diazoalkane completes the catalytic cycle.     

Electrochemical studies of biologically active indolizines

The electrochemical behavior of indolizine ethers, esters, tosylates, sulfonates and other indolizine and azaindolizine derivatives has been investigated by cyclic voltammetry and preparative electrolysis. The cyclic voltammetric data show that the E° values, taken as the midpoints between the anodic and cathodic peak potentials, are sensitive to the identities of the substituents at C-1, C-2 and C-7 positions. The E° values have been correlated with the Hammett substituent parameters. As expected, low E° values are seen for electron donating substituents and higher E° values are seen for electron withdrawing substituents. The cyclic voltammograms of indolizine derivatives with an oxygen atom connected to the C-1 position exhibit a one-electron reversible oxidation and a further, less well-defined, one-electron irreversible oxidation at higher E° values. The cyclic voltammograms of indolizines with hydrogen atom or thienyl substituents connected to the C-1 position exhibit only a one-electron irreversible oxidation. Electrochemical bulk oxidations of indolizines with an oxygen atom at the C-1 position afforded oxoindolizinium salts in decent yields, whereas indolizines with a hydrogen atom at C-1 afforded 1,1′ dimers of indolizines as products in good yields. Bulk oxidation of 1-(α-hydroxybenzyl)-2,3-diphenylindolizine-7-carbonitrile afforded an unexpected ketone product in which the carbonyl group of the indolizine is connected at C-8 instead of at the C-1 position of the starting material. The findings described herein support our hypothesis that certain indolizine derivatives may inhibit lipid peroxidation by an electron transfer mechanism.     

Molecular iodine in isopropenyl acetate (IPA): a highly efficient catalyst for the acetylation of alcohols, amines and phenols under solvent free conditions

Iodine in isopropenyl acetate (IPA) is a highly efficient catalyst for the acetylation of a variety of alcohols, phenols and amines under solvent free conditions. Primary, secondary, tertiary alcohols, amines and mono to polyhydroxy phenols and anilines with electron donating or withdrawing substituents can be easily acetylated in good to excellent yield at 85-90 °C.     

Synthesis of stable isoxazolines by [3+2] cycloaddition of oxaziridines with alkynes

N-Alkyl substituted oxaziridines undergo a [3+2] cycloaddition reaction with a variety of terminal alkynes to give the product isoxazolines, whose stability appears to depend on the electronic properties of the groups on the C-3 and C-5 positions. The presence of an electron withdrawing group on C-5 and/or an electron donating group on C-3 causes isomerization of the isoxazolines to β-amino enones.     

One-pot synthesis of phthalazines and pyridazino-aromatics: a novel strategy for substituted naphthalenes

A new one-pot strategy for the synthesis of phthalazines and pyridazino-aromatics starting from aromatic aldehydes has been developed. A variety of substituents ranging from electron withdrawing to donating is tolerated furnishing the desired 1,2-diazine in good to excellent yields. The products have been applied to the bidentate Lewis acid catalyzed inverse electron-demand Diels-Alder (IEDDA) reaction opening a novel two-step entry into substituted naphthalenes, such as Naproxen.     

Lewis Acid Assisted Brønsted Acid Catalysed Decarbonylation of Isocyanates: A Combined DFT and Experimental Study

An efficient and mild reaction protocol for the decarbonylation of isocyanates has been developed using catalytic amounts of Lewis acidic boranes. The electronic nature (electron withdrawing, electron neutral, and electron donating) and the position of the substituents (ortho/meta/para) bound to isocyanate controls the chain length and composition of the products formed in the reaction. Detailed DFT studies were undertaken to account for the formation of the mono/di-carboxamidation products and benzoxazolone compounds.     

A novel method for the synthesis of dipyrromethanes by metal triflate catalysis

5-Substituted dipyrromethanes were synthesized by the reaction of N-tosyl imines with excess pyrrole in the presence of metal triflates. Tripyrromethane and other oligomeric side products were not observed. High yields of 5-substituted dipyrromethanes were obtained for electron donating and withdrawing substituents by performing the reaction at two different temperatures. The new reaction procedure is simple and anhydrous conditions are not required.     

新型6,6-取代芳基富烯的合成

以取代的芳基酮为原料, 合成了一系列6,6-取代芳基富烯, 这些富烯都经过了核磁共振、元素分析、质谱和红外光谱的鉴定. 芳基酮上的取代基决定了合成中所用碱的类型. 对于含吸电子取代的酮, 采用乙醇钠作为碱可以达到很高的产率, 而对于含烷基等推电子取代的酮, 用环戊二烯基钠直接反应是一种比较好的合成方法.     

Development of one-pot benzylic amination reactions of azine N-oxides

An efficient one-pot synthetic methodology has been developed for the benzylic amination reactions of methyl-substituted azine N-oxides that operate under mild conditions. The reaction was found to tolerate quinoline and isoquinoline N-oxides with electron donating and withdrawing substituents as the electrophilic reaction partners as well as a broad range of nucleophilic primary, secondary and aromatic amines, affording the benzylic amination products in up to 82% yield.     

环状聚茚并茚及其取代衍生物电子结构和磁性研究

采用半经验的AM1法，对环状聚茚并茚及其取代物的电子结构进行了计算研究 ，探讨了其磁性和取代基效应．计算得到，环状聚茚并茚及其取代物皆表现半导体 性质且发现其中一种异构体可能具有磁性．取代基效应表明，吸电子基团的取代使 聚合物的电子亲合势增大，而给电子基团的取代则导致电离势减少，但取代基效应 不能改变聚合物的半导体性质．此外，无论吸电子基团还是给电子基团的取代都不 能改变聚合物的磁性特征．     

Reactions of fluoroalkanesulfonyl azides with pyrrole and its derivatives

The reactions of fluoroalkanesulfonyl azides with pyrrole and its derivatives were studied. The reaction proceeded smoothly under mild conditions to give the 3-(fluoroalkanesulfonamido) pyrroles in good yield. The electron donating groups on the pyrrole core accelerated the reaction, while the electron withdrawing groups decelerated it. All the products were fully characterized by spectrum methods, and one of the products was further confirmed by X-ray diffraction analysis. A possible reaction mechanism for these reactions was proposed.     

Solar energy absorption in norbornadiene-quadricyclane system through electron donating or withdrawing substituents1

An attempt is made to maximize the solar energy absorption in norbornadiene (1)-quadricyclane (2) system, through direct attachment of substituents at C1, C2, or C7 atoms of 1; calculating the corresponding energies at B3LYP/6-311++G** level of theory. The electron donating and electron withdrawing substituents of 1 _n-X, attached at C2, were suitable for both solar absorption bands and solar energy storage. DFT calculations indicate that the solar absorption bands of 1_2-X were shifted to the visible spectrum region through the electron withdrawing substituents more than through electron donating substituents.     

E-Ring extended estrone derivatives: introduction of 2-phenylcyclopentenone to the estrone D-ring via an intermolecular Pauson-Khand reaction

An expedient synthetic route to E-ring extended estrone derivatives is reported. Estrone-derived cyclopentenones were accessed by an intermolecular Pauson-Khand (PK) cycloaddition. It was found that electron donating and withdrawing substituents in the arylalkyne increased and decreased the yields of PK products, respectively. The stereochemistry of the products was elucidated by X-ray and NMR studies.