Preparation of highly substituted 6-arylpurine ribonucleosides by Ni-catalyzed cyclotrimerization. Scope of the reaction

Transition metal complex catalyzed cocyclotrimerization of protected alkynylpurine ribonucleosides 1 with various diynes 2 gave rise to a series of 6-arylpurine nucleosides 3 that were further deprotected to free nucleosides 4. Generally, the best yields of cyclotrimerizations were obtained with a catalytic system Ni(cod)2/2PPh(3). On the other hand, CoBr(PPh(3))3 proved to be a superior catalyst for cyclotrimerization of 1 with dipropargyl ether 2g. In addition, Ni catalysis is also suitable for direct cyclotrimerization of unprotected alkynylpurine ribonucleosides 5 to the corresponding 6-arylpurinylribosides 4.     

Efficient conversion of 6-cyanopurines into 6-alkoxyformimidoylpurines

An extremely simple method for the selective synthesis of 9-aryl and 9-alkyl 6-alkoxy or 6-alkoxyformimidoylpurines from the corresponding 6-cyanopurines is described. The reaction is carried out with methanol or ethanol in the presence of DBU. At room temperature, nucleophilic attack by the primary alcohol occurs selectively on the cyano carbon atom, leading to 6-alkoxyformimidoylpurines in good yields. Heating the reaction mixture at a temperature greater than or equal to 78 degrees C leads to nucleophilic substitution of the substituent in the 6-position by the alkoxy group, generating the corresponding 6-alkoxypurines, also in excellent yields. The 6-alkoxyformimidoylpurines were used as intermediates in the synthesis of 6-carboxamidinopurines by reaction with methylamine (for 9-methylpurine 5a) or methyl ammonium chloride (for 9-arylpurines and 5b and 5c).     

Highly chemo- and regioselective intermolecular cyclotrimerization of alkynes catalyzed by cationic rhodium(I)/modified BINAP complexes

[reaction: see text] Cationic rhodium(I)/modified BINAP complexes are effective catalysts for highly regioselective intermolecular cyclotrimerization of terminal alkynes and highly chemo- and regioselective intermolecular cocyclotrimerization of diethyl acetylenedicarboxylate (DEAD) and terminal alkynes. It is a noteworthy example of intermolecular cocyclotrimerization of two different alkynes in terms of catalytic activity, chemo- and regioselectivity, scope of substrates, and ease of operation. The wide applicability of this new cocyclotrimerization procedure is demonstrated in the one-step synthesis of [6]metacyclophane.     

[2+2+2]-Co-cyclotrimerization 6-alkynylpurines with diynes: a method for preparation of 6-arylpurines

A novel approach to 6-arylpurines based on [2+2+2]-co-cyclotrimerization of 6-alkynylpurines with various α,ω-diynes is described. Co-cyclotrimerization is catalyzed by Ni- and Co-phosphine catalysts and their choice depends on the substitution pattern of the both reactants.     

CuBr catalyzed C-N cross coupling reaction of purines and diaryliodonium salts to 9-arylpurines

CuBr was found to be an efficient catalyst for the C-N cross coupling reaction of purine and diaryliodonium salts. 9-Arylpurines were synthesized in excellent yields with short reaction times (2.5 h). The method represents an alternative to the synthesis of 9-arylpurines via Cu(II) catalyzed C-N coupling reaction with arylboronic acids as arylating agents.     

Microwave promoted palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of 6-chloropurines with sodium tetraarylborate in water

An efficient method for the synthesis of 6-arylpurines (nucleosides) was developed via Suzuki-Miyaura cross-coupling reactions of 6-chloropurines (nucleosides) and sodium tetraarylborate in neat water (ethanol). The process gave good to high isolated yields within a short reaction time under microwave irradiated conditions.     

Pd(II)-catalyzed ortho arylation of 6-arylpurines with aryl iodides via purine-directed C-H activation: a new strategy for modification of 6-arylpurine derivatives

Purine is utilized as a new directing group for the Pd-catalyzed monoarylation of 6-arylpurines with simple aryl iodides via C-H bond activation in good yields, providing a complementary tool for the modification of 6-arylpurines (nucleosides). Most importantly, purine can be used as a building block for nucleoside derivatives, and the use of purine as a directing group helps avoid additional synthetic steps.     

Synthesis and in vitro activity of 6-amino-2,9-diarylpurines for Mycobacterium tuberculosis

A mild method was developed to synthesize 6-amino-2-phenolic-9-alkyl and 9-arylpurines. The new compounds were screened for antibacterial activity against Mycobacterium tuberculosis strain H₃₇Rv. The 9-tolyl derivatives with a dimethylamino or a piperidine substituent in C6 and the 3-hydroxyphenyl or 4-hydroxyphenyl substituent in C2 were highly active against the bacilli.     

阳离子表面活性剂存在下水/有机两相体系中双环戊二烯氢甲酰化

研究了在阳离子表面活性剂存在下水/有机两相中水溶性铑配合物RhCI(CO)(TPPTS)2(TPPTS:P(m-C6H4SO3Na)3)催化双环戊二烯氢甲酰化反应,考察了反应温度、催化剂浓度、不同水溶性膦配体TPPTS和TPPDS(C5H5P(m-C6H4SO3Na)2),以及表面活性剂结构对催化反应的影响.结果表明,...     

MgCl(2).6PhCH2OH--a new molecular adduct as support material for Ziegler-Natta catalyst: synthesis, characterization and catalytic activity

Benzyl alcohol has been used to prepare a single phase MgCl(2).6BzOH molecular adduct as a support for an ethylene polymerization catalyst (Ziegler catalyst). The structural, spectroscopic and morphological aspects of the MgCl(2).6BzOH molecular adduct and the Ziegler catalyst have been thoroughly studied by various physicochemical characterization techniques. The presence of MgO(6) octahedrons due to the interaction of Mg(2+) with six -OH groups of the benzyl alcohol is confirmed from a Raman feature at 703 cm(-1), and structural studies. The supported catalyst activity has been evaluated for the ethylene polymerization reaction. The lower polymerization activity of the titanated Ziegler-Natta catalyst compared with a standard catalyst is attributed to the strong interaction of titanium chloride with the support and associated electronic factors.     

Palladium-catalyzed [2 + 2 + 2] cocyclotrimerization of benzynes with bicyclic alkenes: an efficient route to anellated 9,10-dihydrophenanthrene derivatives and polyaromatic compounds

An efficient method for the cocyclotrimerization of bicyclic alkenes and benzynes catalyzed by palladium phosphine complexes to give the corresponding norbornane anellated 9,10-dihydrophenanthrene derivatives is described. Bicyclic alkenes 1a-i undergo [2 + 2 + 2] cocyclotrimerization with benzynes generated from precursors 2a-d [2-(trimethylsilyl)phenyl triflate (2a), 4,5-dimethyl-2-(trimethylsilyl)phenyl triflate (2b), 6-(trimethylsilyl)-2,3-dihydro-1H-5-indenyl triflate (2c), 4-methyl-2-(trimethylsilyl)phenyl triflate (2d)] in the presence of PdCl(2)(PPh(3))(2) in acetonitrile at ambient temperature to yield anellated 9,10-dihydrophenanthrene products 3a-r in moderate to excellent yields. The [2 + 2 + 2] cocyclotrimerization products from oxa- and azabicyclic alkenes can be applied for the synthesis of polyaromatics, substituted benzo[b]triphenylenes (8a-f), via a simple Lewis acid mediated deoxyaromatization in good yields. In addition the [2 + 2 + 2] products undergo retro Diels-Alder reaction readily, providing a new method for the synthesis of substituted phenanthrenes and for generating isobenzofurans. A plausible mechanism is proposed to account for the catalytic [2 + 2 + 2] cycloaddition reaction.     

Facile synthesis of 6-aryl 5-N-substituted pyridazinones: microwave-assisted Suzuki-Miyaura cross coupling of 6-chloropyridazinones

A facile synthesis of 5-dialkylamino-6-aryl-(2H)-pyridazin-3-one from 5,6-dichloropyridazinone was carried out by using a palladium-catalyzed Suzuki-Miyaura cross coupling of 6-chloro-5-dialkylaminopyridazinone 1 with various arylboronic acids (3 equiv) as the key transformation. The Suzuki-Miyaura cross-coupling reaction proceeded smoothly under microwave irradiation at 135-140 degrees C for 30 min with 5 mol % of Pd catalyst in moderate to good isolated yields. The use of a CombiPhos Pd6 mixture catalyst system and a single Pd-SPhos catalyst system was evaluated.     

New bis(N‐heterocyclic carbene) palladium complex immobilized on magnetic nanoparticles: as a magnetic reusable catalyst in Suzuki‐Miyaura cross coupling reaction

A new bis(N ‐heterocyclic carbene) (NHC) palladium complex supported on silica coated magnetic nanoparticles (MNPs) was prepared using the reaction of synthesized Pd‐NHC complex with MNPs. The Pd‐NHC complex was prepared using the reaction of a hydroxyl‐functionalized bis‐imidazolium ionic liquid. The Pd‐NHC organometallic complex was used as a heterogeneous recyclable and active catalyst in the Suzuki‐Miyaura reaction and various aryl halides were coupled with arylboronic acids in order to synthesize diverse biaryls in good to excellent yields. The prepared catalyst was characterized by use of some different microscopic and spectroscopic techniques including elemental analysis, FT‐IR spectroscopy, diffuse reflectance UV–Vis spectrophotometery, scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and X‐ray diffraction (XRD). The Pd‐NHC catalyst system is a magnetic reusable catalyst and it can be separated from the reaction mixture using an external magnetic field. The catalyst was reusable in the Suzuki‐Miyaura coupling reaction at least for 6 times without significant decreasing in its catalytic activity.     

(PPh3)Ag(CB11H6Y6)] (Y = H,Br): highly active,selective and recyclable Lewis acids for a hetero-Diels-Alder reaction

The complex [(PPh3)Ag(CB11H6Br6)] 1 is an effective and selective catalyst (0.1 mol% loading) for a hetero-Diels-Alder reaction, which shows a marked dependence on the presence of trace amounts of water, while addition of Ag[Y] [Y = CB11H12, CB11H6Br6, O3SCF3] to a phosphine functionalized support gives an efficient and recyclable Lewis acid catalyst for this transformation.     

Mechanism of silver(I)-catalyzed Mukaiyama aldol reaction: active species in solution in AgPF6-(S)-BINAP versus AgOAc-(S)-BINAP systems

Silver(I)-diphosphine complex is an effective catalyst for Mukaiyama Aldol reaction in polar solvents. AgPF₆-(S)-BINAP cationic chiral complex indicated a good activity and could afford fairly high enantioselectivity in the reaction of aromatic aldehydes and silyl enol ethers. On the other hand, AgOAc-(S)-BINAP system afforded the aldol product of the absolute configuration opposite to that by AgPF₆-(S)-BINAP and very high catalytic activity was shown. The structure and equilibrium state of Ag(I)-BINAP complexes in solution were examined to understand the reaction mechanism. In AgPF₆ system [Ag((S)-BINAP)₂]PF₆ (1a), [Ag((S)-BINAP)]PF₆ (1b), [Ag₂((S)-BINAP)](PF₆)₂ (1c) and AgPF₆ are present in solution. The active species of the aldol reaction in DMF is [Ag((S)-BINAP)]PF₆ (1b), which exists as a minor species in solution. For this cationic Ag(I) catalyst, cyclic transition state containing substrate and silyl enol ether is assumed. In AgOAc-(S)-BINAP system, active species is also monomeric AgOAc((S)-BINAP) (2b) species which exists as a major component in solution and strong interaction was observed with a silyl enol ether. The reaction by AgOAc-(S)-BINAP catalyst is concluded to proceed as follows: nucleophile forms a complex with AgOAc-(S)-BINAP species and is activated. This complex attacks aldehydes to afford aldol adduct via acyclic transition state.     

Phenol-containing macrocyclic diamides as new catalysts in the highly regioselective conversion of epoxides to beta-hydroxy thiocyanates.

The regioselective ring-opening reactions of some epoxides with ammonium thiocyanate in the presence of a series of new phenol-containing macrocyclic diamides and also dibenzo-18-crown-6-, 18-crown-6-, benzo-15-crown-5-, and pyridine-containing macrocyclic diamide have been studied. The epoxides were subject to cleavage by NH(4)SCN in the presence of these catalysts under mild reaction conditions in various aprotic solvents. In this study, reagents and conditions have been discovered with which the individual beta-hydroxy thiocyanates can be synthesized in high yield and with more than 90% regioselectivity. The results can be discussed in terms of a four-step mechanism: (1) formation of complex between catalyst and NH(4)SCN, (2) release of SCN(-) nucleophile from the complex, (3) reaction of the active nucleophile at the less sterically hindered site in the epoxide, and (4) regeneration of catalyst. The major advantages of this method are as follows: (1) high regioselectivity, (2) simple regeneration of catalyst, (3) its reuse through several cycles without a decrease in activity, and (4) ease of workup of the reaction.     

The Synthesis and Bioactivity of Dimethyl (2,3- Dihydrobenzo[b][1,4]Dioxin-6-Yl)(Aryl Amino)Methylphosphonates

Abstract

A new series of α-aminophosphonates have been synthesized by a one-pot three-component reaction of 2,3-dihydrobenzo[b][1,4]dioxine-6-carbaldehyde, various amines, and dimethyl phosphite by using nano-TiO₂ as a catalyst under solvent-free conditions at 50°C. The major advantages of the present method are high yields, short reaction times, recyclable catalyst, and solvent-free reaction conditions. Among these new structurally diversified set of α-aminophosphonates, dimethyl (2,3-dihydrobenzo[b][1,4]dioxin-6-yl)(3-nitrophenylamino) methylphosphonate and dimethyl (2,3-dihydrobenzo[b][1,4]dioxin-6-yl)(4-fluoro-3-nitro-phenyl-amino) methylphosphonate have shown higher antioxidant activity in diphenyl picryl hydrazyl (DPPH) scavenging, reducing power assay, and lipid peroxidation methods.     

Nickel-catalyzed highly chemoselective cocyclotrimerization of arynes with allenes: a novel method for 10-methylene-9,10-dihydrophenanthrenes

The NiBr(2)(dppe)-Zn system effectively catalyzes the [2+2+2] cocyclotrimerization of arynes with allenes, leading to 10-methylene-9,10-dihydrophenanthrenes in moderate to good yields. The cocyclotrimerization is highly selective with only the internal double bond of the allenes being involved in the reaction.     

Nickel-catalyzed cocyclotrimerization of arynes with diynes; a novel method for synthesis of naphthalene derivatives

The NiBr2(dppe)-Zn system effectively catalyzes the [2 + 2 + 2] cocyclotrimerization of arynes with diynes, leading to substituted naphthalene derivatives in moderate to good yields. This cocyclotrimerization reaction shows excellent tolerance of functional groups and leads to products of 5- to 7-membered fused-ring sizes.     

柠檬酸辅助水热法制备可见光高效去除甲基橙的Bi2WO6纳米片

以Bi(NO3)3·5H2O和Na2WO3 ·2H2O为原料,以柠檬酸为络合剂,采用辅助水热法制备了Bi2WO6纳米片,运用X射线衍射、扫描电镜、场发射高分辨透射电镜、拉曼光谱、红外光谱和紫外-可见漫反射光谱等手段对样品进行了表征,并考察了该催化剂光催化去除甲基橙反应性能.结果表明,通过调节体系的pH值可制得结晶度良好...