Regioselective and Regiospecific Cycloaddition of Acetylenes to 2,4,6-Triazidopyridine

The cycloaddition of tert-butylacetylene to 2,4,6-triazido-3,5-dicyanopyridine and 2,4,6-triazido-3-chloro-5-cyanopyridine occurs regioselectively and regiospecifically at the azide group in position 4 of the pyridine ring leading to the formation of the corresponding 4-(4'-tert-butyl-1H-1,2,3-triazolyl)pyridines as the sole products. Analogous reactions with the less sterically hindered n-butylacetylene are characterized by less regiospecificity and give a mixture of the isomeric 4'- and 5'-n-butyl-substituted triazoles at ratios of 96 : 4 and 91 : 9 respectively for the two different triazides. The interaction energies of the pyridine - and -azide groups with the acetylene molecules, and the energies of the transition states for these reactions have been calculated by the PM3 method. It was established that the high reactivity of the -azide group of the triazidopyridines in relation to the! ace tylenes is caused by the anomalously low distribution of bonding orbital density on these groups, leading to substantially lower activation energies in 1,3-dipolar cycloaddition reactions.     

Stereo- and regioselective cycloaddition of norbornene to 2,4,9-triazidopyridine

4-(3-Azatricyclo[3.2.1.0]oct-3-yl)-2,6-diazido-3,5-dicyanopyridine has been obtained by the reaction of 2,4,6-triazido-3,5-dicyanopyridine with an equimolar quantity of norbornene. The product reacted readily at room temperature with an excess of norbornene giving the corresponding trisazatricyclooctane cycloadduct. An analogous trisadduct was obtained in the reaction of 4-(3-azatricyclo[3.2.1.0]oct-3-yl)-1,6-diazido-3-chloro-5-cyanopyridine with norbornene on boiling in CCl₄, and also in ether at room temperature in the presence of the complexes Rh₂(OAc)₄ and Cu(AcAc)₂. The cycloaddition proceeds stereoselectively in all cases with the exclusive formation of exo-conformers. Calculations have been carried out using the PM3 and RHF/3-21G^* methods on 2,4,6-triazido-3-chloro-5-cyanopyridine and on 2,4,6-triazido-3,5-dicyanopyridine and also on the cycloadducts of these compounds with one or two molecules of norbornene. It was established that the addition of norbornene at the azide groups of pyridine is a dipole-LUMO controlled type of reaction and leads to the formation of cycloadducts having higher LUMO energy than the initial azides. The energy of the LUMO is increased to a lesser extent as a result of the addition of norbornene to a triazide containing identical substituents in the β positions of the pyridine ring, and is due to the special features of the symmetry of the LUMO of the cycloadducts formed. Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, Chernogolovka 142432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1521–1532, November, 1997.     

Reactions of dialkyl (3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-4-oxocyclohex-2,5-dienylidenemethyl)phosphonates with alcohols and some transformations of the adducts

Reactions of dialkyl [(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)methyl]phosphonates with butyl, benzyl and propargyl alcohols in the presence of catalytic amounts of trifluoromethanesulfonic acid resulted in the formation of nucleophilic 1,6-addition products. Azide-alkyne cycloaddition reaction of dimethyl (3,5-di-tert-butyl-4-hydroxyphenyl)(prop-2-ynyloxy)methylphosphonate with benzyl azide and 1,3-bis-(2-azidoethoxy)benzene in the presence of copper sulfate and sodium ascorbate afforded 1,2,3-triazoles with sterically hindered phenol fragments.     

Novel first-generation dendrimers on calix[4]resorcinol core equipped with multiple triazole units

Novel first-generation dendrimers on the calix[4]resorcinol core with four branches each containing multiple 1,2,3-triazole units have been synthesized in one-step by acid catalyzed condensation of resorcinols with a new aldehyde dendron, namely, 4-{3,5-bis[(1-benzyl-1H-1,2,3-triazol-4-yl)- methoxy]benzyloxy}benzaldehyde (obtained by alkyne–azide cycloaddition). The reaction proceeds stereoselectively to form rccc-diastereoisomers in high yields.     

Application of Hantzsch Dihydropyridine in Copper-Catalyzed [3 + 2] Cycloaddition of Terminal Alkynes with Azides

2,6-Dimethyl-3,5-bis(ethoxycarbonyl)-1,4-dihydropyridine (dihydropyridine Hantzsch ester, DHPHE) and CuSO₄ · 5H₂O efficiently accelerated azide–alkyne cycloaddition reactions of both aliphatic and aromatic substrates and gave 1,4-disubstituted 1,2,3-triazoles as the only isomer in good to excellent yields at room temperature with 1 mol% of CuSO₄ · 5H₂O/DHPHE (1:1 in molar ratio). The reaction could be carried out smoothly in methanol in air with high efficiency. DHPHE may play multiple important roles in the reaction: a reducing reagent to generate the catalytic center copper(I) from CuSO₄, a base to help form the intermediate acetylide, and a ligand to stabilize the catalytic copper(I) species via coordination after being transformed to pyridine derivative.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

4,4-dimethyl-4,5-dihydro-1,2-dithiolo-[3,4-c]quinoline-1-thiones in 1,3-dipolar cycloaddition reactions with acetylenic dipolarophiles

The behavior of 4,4-dimethyl-4,5-dihydro-1,2-dithiolo[3,4-c]quinoline-1-thiones in the 1,3-dipolar cycloaddition reaction with acetylenic dipolarophiles has been studied. The rate of cycloaddition is reduced along with the decrease of electron-deficiency of the triple bond. Substituted 4-(1′,3′-dithiol-2′-ylidene)-1,2-dihydroquinoline-3-thiones were shown to be the reaction products. On using a twofold excess of acetylenedicarboxylic acid dimethyl ester, adducts of composition 1∶2 were formed which occured to be substituted 1′, 3′-dithiole-2′-spiro-1-(5,6-dihydrothiino[2,3-c]quinolines). Voronezh State University, Voronezh 394693, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 656–660, May, 1999.     

Three-component reaction of 5-aryl-4-(quinoxalin-2-yl)-furan-2,3-diones,acetylenedicarboxylic acid dimethyl ester,and triphenylphosphine

Three-component synthesis from 5-aryl-4-(quinoxalin-2-yl)furan-2,3-diones, acetylenedicarboxylic acid dimethyl ester, and triphenylphosphine afforded methyl esters of 1,6-dioxaspiro[4.4]nona-3,7-diene-4-carboxylic and 4H-furo[3,2-c]pyran-3-carboxylic acids.     

Novel Hyperbranched Poly([1,2,3]‐triazole)s Derived from AB2 Monomers by a 1,3‐Dipolar Cycloaddition

Summary: Novel hyperbranched poly([1,2,3]‐triazole)s were synthesized from several AB₂ monomers by a 1,3‐dipolar cycloaddition reaction. The compound 3,5‐bis(propargyloxy)benzyl azide was polymerized thermally at room temperature leading to 1,4‐ and 1,5‐disubstituted poly([1,2,3]‐triazole) and catalytically leading only to the 1,4‐disubstituted poly([1,2,3]‐triazole). Only the thermal reaction led to fully soluble products. The AB₂ monomers containing an internal alkyne A unit could be autopolymerized thermally under mild reaction conditions leading to soluble, high‐molecular‐weight hyperbranched poly([1,2,3] triazole)s. All products were characterized by detailed NMR investigations.

Synthesis route for polymers 8a and 8b .     

The reaction of ethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate with fullerene C60

Heating (100 °C, toluene) or photolysis (Nd³⁺ : YAG laser, = 532 mil, benzonitrile) of a mixture of ethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate (Hantsch ester) (1) and fullerene C₆₀ under anaerobic conditions results in the formation of fullerene hydrogenation products and ethyl 2,6-dimethylpyridine-3,5-dicarboxylate, which is the product of dehydrogenation of1, identified by IR spectroscopy and mass spectrometry. The triplet state of C₆₀ is quenched by the Hantsch ester.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2531–2534, October, 1996.     

Selective Thermolysis of Azide Groups in 2,4,6-Triazidopyridines

When refluxed in 1,4-dichlorobenzene, the compound 2,4,6-triazido-3,5-dichloropyridine and its 3,5-dicyano derivative undergo selective thermolysis of the -azide groups, forming the corresponding 4-amino-2,6-diazidopyridines in high yields. According to quantum-chemical calculations, the selectivity of thermolysis of the -azide groups in triazides is due to the weaker bonding interactions between the N₍₎ and N₍₎ atoms in these azide groups.     

Nitropyrazoles: XII. Transformations of the 4-Methyl Group in 1,4-Dimethyl-3,5-dinitropyrazole and Cyclization of the Transformation Products

A preparative procedure for the synthesis of 1,4-dimethyl-3,5-dinitropyrazole by nitration of 1,4-dimethylpyrazole was developed. The reaction of 1,4-dimethyl-3,5-dinitropyrazole with dimethoxymethyl- (dimethyl)amine (N,N-dimethylformamide dimethyl acetal) gave (E)-N,N-dimethyl-2-(1-methyl-3,5-dinitropyrazol- 4-yl)ethenylamine. Acid hydrolysis of the latter afforded (1-methyl-3,5-dinitropyrazol-4-yl)acetaldehyde, and the reaction with sodium nitrite in hydrochloric acid led to formation of 2-hydroxymino-2-(1-methyl- 3,5-dinitropyrazol-4-yl)acetaldehyde. The corresponding O-methyloxime and phenylhydrazone reacted with K₂CO₃ to give 6-methyl-4-nitropyrazolo[4,3-d]isoxazole-3-carbaldehyde O-methyloxime and 1-methyl-3-nitro-4-(2-phenyl-2H-1,2,3-triazol-4-yl)pyrazol-5-ol, respectively. Treatment of (1-methyl-3,5-dinitropyrazol-4-yl)-acetaldehyde with benzenediazonium chloride gave (1-methyl-3,5-dinitropyrazol-4-yl)acetaldehyde phenylhydrazone which underwent intramolecular cyclization with replacement of the 5-nitro group by the action of K₂CO₃ in acetonitrile; in the reaction with K₂CO₃ in ethanol, the 5-nitro group was replaced by ethoxy.     

新型S(N)-β-D-葡萄糖苷-4-N-(取代邻羟苯基)亚胺基-5-(4-甲基-1,2,3-噻二唑)-1,2,4-三唑的合成及生物活性

在KOH/acetone体系中,4-N-(取代邻羟苯基)亚胺基-5-(4-甲基-1,2,3-噻二唑)-1,2,4-三唑-3-硫酮(3a～3d)与溴-α-D-四乙酰葡萄糖发生Kenigs-Knorr反应,合成了8个未见报道的S(N)-β-D-乙酰葡萄糖苷,其结构经1H NMR、13C NMR、红外光谱及元素分析等确定.目标化合物的生物活性测试结果表明,它们对金黄色葡萄球菌、白色念珠菌和大肠杆菌均显示了较好的抑菌活性,其效果接近或优于对照药物三氯生和氟康唑的抑菌效能.其中,化合物2-N-(2’,3’,4’,6’-O-四乙酰基-β-D-吡喃葡萄糖基)-4-N-(3,5-二溴邻羟苯基)亚胺基-5-(4-甲基-1,2,3-噻二唑)-1,2,4-三唑-3-硫酮(4d)及3-S-(2’,3’,4’,6’-O-四乙酰基-β-D-吡喃葡萄糖硫基)-4-N-(3,5-二溴邻羟苯基)亚胺基-5-(4-甲基-1,2,3-噻二唑)-1,2,4-三唑(5d)具有较强的抑菌活性.     

The first example of the generation of azomethine ylides from a fluorocarbene: 1,3-cyclization and 1,3-dipolar cycloaddition

The reaction of Schiff bases with fluorocarbene, generated by reduction of dibromofluoromethane with active lead in the presence of Bu₄NBr under ultrasound irradiation, involves the formation of fluoro-substituted azomethine ylides which undergo cyclization into aziridines. 1,3-Cyclization of ylides, generated from N-arylimines of benzaldehyde, proceeds stereoselectively. When carrying out the reaction of Schiff bases with fluorocarbene in the presence of dimethyl maleate or dimethyl acetylenedicarboxylate, the products of dehydrofluorination of the primary adducts of the 1,3-dipolar cycloaddition of fluoro-substituted azomethine ylides to multiple bonds of dipolarophiles were obtained. In the case of the reaction of N-alkylimines of benzaldehyde the cycloaddition of ylides to dimethyl maleate completely suppressed the cyclization to aziridines.     

Nickel(II) Complexes Bearing 4-Arylimino-1,2,3-trihydroacridines: Synthesis,Characterization, and Ethylene Oligomerization

Nickel(II) complexes have attracted much attention as a new generation of olefin catalysts since the α-diiminonickel complex was discovered as a highly efficient procatalyst for ethylene polymerization. A series of novel 4-arylimino-1,2,3-trihydroacridylnickel(II) dihalide complexes was synthesized in a one-pot reaction of 2,3-dihydroacridine-4-one and different anilines with nickel(II) chloride or nickel(II) bromide 1,2-dimethoxyethane complex. The complexes were characterized by infrared spectroscopy and elemental analysis. The molecular structures of the representative complexes 4-(2,6-diisopropylphenylimino)-1,2,3-trihydroacridylnickel(II) dichloride (C3), 4-(2,4,6-trimethylphenylimino)-1,2,3-trihydroacridylnickel dichloride(II) (C4), and 4-(2,4,6-trimethylphenylimino)-1,2,3-trihydroacridylnickel(II) dibromide (C9) were confirmed by single-crystal X-ray crystallography, revealing a distorted tetrahedral geometry around the nickel(II) of C3 and distorted trigonal bipyramidal geometry for C4 and C9. With the activation of trimethylaluminium (TMA), all nickel(II) complexes exhibited good activity for ethylene oligomerization, and oligomer products ranged from butene (C₄) to hexadecene (C₁₆).     

MeOPEG-bounded azide cycloadditions to alkynyl dipolarophiles

The MeOPEG-supported azide 2 was reacted in the presence of a number of alkynyl dipolarophiles. The corresponding 1-MeOPEG-supported-1,2,3-triazoles were obtained in nearly quantitative yields. Acidic hydrolysis of the cycloadducts 5b and 6b caused the removal of the MeOPEG pendant giving 4-methoxycarbonyl-1,2,3-triazole 9 and 5-methoxycarbonyl-1,2,3-triazole 10, respectively.     

Synthesis of Isomeric Dimers of Deoxycholic Acid Derivatives Linked by 1,2,3-Triazole

Steroidal propargylic ester 6 and the propiolic ester 7 were prepared in a few steps from the deoxycholic acid. The Huisgen cycloaddition reaction of alkynes 6 and 7 as dipolarophiles with a 1,3-dipolar compound, the azide 5, afforded the dimeric compounds 8 and 9, respectively, in good yield. The dimers of deoxycholic acid derivatives linked by 1,4-disubstituted 1,2,3-triazole were characterized by spectroscopic methods.     

1,3-Dipolar cycloadditions of MeOPEG-bounded azides

1,3-Dipolar cycloadditions of MeOPEG-supported azide 2 with a variety of dipolarophiles have been studied. 1-MeOPEG-supported 1,2,3-triazoles 4 and 5, 1,2,3,4-tetrazoles 12 and aziridine 14 were obtained in nearly quantitative yields. The removal of the MeOPEG moiety from the 1,2,3-triazole nucleus was achieved by acidic cleavage of the cycloadduct mixtures 4 and 5 giving 4- and 5-substituted-1,2,3-triazoles 6 and 7.     

Trimethylsilyl-directed 1,3-dipolar cycloaddition reactions in the solid-phase synthesis of 1,2,3-triazoles

[reaction: see text] A regioselective method for the preparation of 1,5-trisubstituted 1H-1,2,3-triazoles via a 1,3-dipolar cycloaddition of 1-trimethylsilylacetylenes with organoazides is described. Immobilization of the azide on REM resin and subsequent cycloaddition afforded a 2 x 2 x 4 x 3 membered 1,5-disubstituted 1H-1,2,3-triazole library with an average purified yield of 68%.     

Tetraphenylbismuth aroxides: Synthesis and structure

Tetraphenylbismuth aroxides Ph4BiOAr (Ar = C₆H₃Cl₂-2,6, C₆H₂(Br₂-2,6)(t-Bu)-4, C₆H₂(Br₂-2,6)(NO₂)-4 · 1/2C₆H₆, C₆H₃(NO₂)₂-2,4, C₆H₂(NO₂)₃-2,4,6) were synthesized in the yield up to 90% by the reaction of pentaphenylbismuth with phenols and triphenylbismuth diaroxides and studied by X-ray diffraction. The Bi atoms of tetraphenylbismuth aroxides have a distorted trigonal-bipyramidal coordination with the axial O atom of the aroxide group. The axial angles CBiO vary from 171.7(2)° to 179.3(3)°. The distances Bi-O change in the interval 2.453(2)–2.925(7) Å depending on the nature of substituents in the aromatic ring of the phenol residue. The increasing distance Bi-O in the series of compounds under study correlates with the tendency of the BiC₄ fragment to form the tetrahedral configuration.     

Bromination and Azidation Reactions of 2-Styrylchromones. New Syntheses of 4(5)-Aryl-5(4)-(2-chromonyl)-1,2,3-triazoles

The bromination of 2-styrylchromones, bearing electron neutral substituents, with two molar equivalents of piridinium tribromide gave 2-(2-aryl-1,2-dibromoethyl)chromones and 3-bromo-2-(2-aryl-1,2-dibromoethyl)chromones. The presence of electron-donating substituents on their B ring led to a mixture of compounds due to the higher reactivity of their C(2)=C(3) and C=C double bonds, whereas the strongly electron-withdrawing group hindered the bromination. The dehydrobromination of 2-(2-aryl-1,2-dibromoethyl)chromones with triethylamine gave a diastereomeric mixture of (E)- and (Z)-2-(-bromostyryl)chromones. Some novel 4(5)-aryl-5(4)-(2-chromonyl)-1,2,3-triazoles have been obtained from the reactions of 2-(2-aryl-1,2-dibromoethyl)chromones, 2-(-bromostyryl)chromones, and 2-styrylchromones with sodium azide. The reactions of 2-styrylchromones with sodium azide are more efficient, general, and constitute a one-pot synthetic method of 4(5)-aryl-5(4)-(2-chromonyl)-1,2,3-triazoles allowing the preparation of 1,2,3-triazoles bearing either electron-donating or electron-withdrawing substituents in their aryl ring. The structure of all new compounds was established by extensive NMR spectroscopic studies.