alpha,5-didehydro-3-picoline diradicals from skipped azaenediynes: computational and trapping studies of an aza-Myers-Saito cyclization

[reaction: see text] On the basis of density functional calculations, the isomerization of skipped azaenediynes (C-alkynyl-N-propargylimines) to azaenyne allenes and subsequent rapid aza-Myers-Saito cyclization to alpha,5-didehydro-3-picoline were predicted. We prepared the N-propargylimine of 1-phenyl-3-tri(isopropyl)silylprop-2-yn-1-one, which undergoes proto-desilylation and isomerization to an azaenyne allene when treated with tetrabutylammonium fluoride. In the presence of 1,4-cyclohexadiene, this azaenyne allene affords 6-phenyl-3-picoline and other products corresponding to the trapping of an alpha,5-didehydro-3-picoline diradical.     

Palladium-catalyzed regioselective silaboration of pyridines leading to the synthesis of silylated dihydropyridines

The addition of silylboronic esters to pyridine takes place in toluene at 50 °C in the presence of a palladium catalyst to give N-boryl-4-silyl-1,4-dihydropyridines in high yield. The regioselective 1,4-silaboration also proceeds in the reaction of 2-picoline and 3-substituted pyridines, whereas 4-substituted pyridines undergo 1,2-silaboration to give N-boryl-2-silyl-1,2-dihydropyridines regioselectively.     

Potential histidine decarboxylase inhibitors. II. 3-(4-Imidazolyl)-2-pyridine and piperidinecarboxylates

The synthesis of methyl 3-(4-imidazolyl)-2-pyridine ( 12 ) and piperidineearboxylates ( 13 ) is described. Hydrolysates of these esters were found to be devoid of inhibitory activity against histidine decarboxylase. 3-Bromoacetyl-2-pieoline ( 2 ) could be converted to 3-(4-imidazolyl)-2-picoline ( 6 ) by two different routes. Treatment of 6 with peroxide and acetic anhydride, followed by transesterification yielded the 2-hydroxymcthyl pyridine ( 9 ). Oxidation of 9 followed by esterification gave the imidazole pyridine acid ester ( 12 ) which after hydrogenation afforded the imidazolylpiperidine ester ( 13 ).     

Lithium n-benzyltrimethylsilylamide (LSA): a new reagent for conjugate addition - enolate trapping reactions

Lithium N-benzyltrimethylsilyl amide (LSA) adds to crotonates in a 1,4-manner, though the reaction of ordinary lithium amides with α,β-unsaturated carbonyl compounds is accompanied with a 1,2-addition and hydrogen abstraction at the γ-position. The conjugate addition via LSA followed by enolate trapping with electrophiles produces the corresponding α-substituted β-amino esters, which are, in turn, converted into β-lactams and α-substituted α, β-unsaturated esters.     

Relaxation dynamics of highly vibrationally excited picoline isomers (E(vib) = 38 300 cm(-1)) with CO2: the role of state density in impulsive collisions

Strong collisions of highly vibrationally excited picoline isomers and CO2 (00(0)0) were investigated using high resolution transient IR absorption probing to investigate the role of donor state density. Vibrationally excited 3-picoline and 4-picoline (3-methylpyridine and 4 methylpyridine) with E(vib) = 38300 cm(-1) were prepared by 266 nm excitation followed by rapid internal conversion. Transient IR probe measurements of the nascent rotational and translational energy gain in CO2 (00(0)0) show that large DeltaE collisions for 3- and 4-picoline are similar to those for excited 2-picoline. The probability distributions for the large DeltaE energy transfer of the three isomers have similar dependence on DeltaE. The results are compared with other earlier results demonstrating that the shape of the large DeltaE probability distribution correlates with the DeltaE dependence of the donor vibrational state density. The results are discussed in terms of the GRETCHEN model for collisional relaxation.     

Convenient Preparation of Cycloalkenyl Boronic Acid Pinacol Esters

A practical method for the preparation of cycloalkenyl boronic acid pinacol esters is described. These important synthetic intermediates are typically made using more expensive methods like transition metal-catalyzed borylation of alkenyl halides or triflates. In this work, they are obtained from the simple corresponding cycloalkanones, which are subjected to Shapiro reaction conditions followed by trapping with a borate ester. The requisite products are obtained in very good to excellent yields, and the reactions can be scaled up to multigram amounts. By providing a simple alternative to common methods that make use of expensive transition-metal catalysts and formation of sensitive intermediates, this convenient method will be useful for the synthesis of ring-containing partners for Suzuki–Miyaura cross-coupling and other reactions employing boronic esters as substrates.     

Additionen von Stickstoffbasen an cyclische Organoborsäureester

Additive-Reactions of Nitrogen Bases to Cyclic Esters of Organoboric Acids The reaction of BBr₃, C₆H₅BCl₂ and CH₃BBr₂ with Diols respectively Dithiols yields 2-Bromo- and 2-Organo-1,3,2-diheteroborolanes, -borinanes and -boroles. These compounds and also non cyclic esters and thioesters of organoboric acids are reacted with pyridine, 2-picoline, 4-picoline and 2,4,6-collidine and thereby the enthalpie (ΔH) is measured. From these values it is tried to conclude on Lewis acidity of the boron atom in the different compounds.     

Thermochemical Kinetics of Nitrogen Compounds. Part 4. The gas phase unimolecular thermal decomposition of triallylamine

The gas phase thermal decomposition of triallylamine was studied in the temperature range 531 to 620 K. The major products observed in the reaction were propylene and 3-picoline. The first order rate constants for depletion of triallylamine, obtained using the internal standard technique, are found to be independent of pressure and conversion, and fit the Arrheniusrelationship The reaction appears to be homogeneous, as a 15-fold change in thc surface-to-volume ratio of the vessel left the rate constants unchanged. The Arrhenius parameters are consistent with a molecular elimination reaction involving a six-center transition state, yielding propylene and N-allyl-prop-2-enaldimine. It is proposed that the latter product undergoes a 1,5-hydrogen transfer, followed by a ring closure reaction to yield dihydropicoline, which in turn reacts forming 3-picoline via a self-initiated decomposition reaction.     

Making thiamin work faster: acid-promoted separation of carbon dioxide

The conjugate of thiamin and benzoylformate, mandelylthiamin (MTh), undergoes decarboxylation about 106 times slower than the analogous enzymic intermediate. It has now been discovered that the decarboxylation of MTh is accelerated by the acid component of pyridine and 4-picoline buffers. There is no role for a proton donor to stabilize the transition state for decarboxylation: catalysis must be achieved by the acid's trapping the product carbanion, preventing recarboxylation. This requires that diffusion of CO2 is rate-determining, and that protonation of the carbanion allows this to occur. This interpretation correctly predicts that the same acid components will prevent a fragmentation reaction by protonating the intermediate, which fragments only as the conjugate base.     

A novel one-step synthesis of 2-substituted 6-azaindoles from 3-amino-4-picoline and carboxylic esters

Dilithiation of 3-amino-4-picoline (1) was achieved with sec-BuLi at room temperature. Condensation of the resulting dianion (2) with carboxylic esters afforded a wide range of 2-substituted 6-azaindoles in good yields.     

Polymer heterogenized iridium amino complexes. Catalyzed reduction of nitrobenzene under WGSR conditions

The activation studies for catalytic reduction of nitrobenzene to aniline by iridium(I) complexes, [Ir(COD)(amine)₂]PF₆ (COD=1,5-cyclooctadiene, amine =4-picoline, 3-picoline, 2-picoline, or pyridine) heterogenized on poly(4-vinylpyridine) in aqueous 2-ethoxyethanol are described. The aniline formation (mmol, based on CO₂ formed after 9 h) followed the order: 4-picoline (0.068)>2-picoline (0.052)>3-picoline (0.046)≥pyridine (0.042) for 1.0×10⁻⁴ mol Ir/0.5 g of polymer, 0.26 mL of nitrobenzene, 10 mL of 2-ethoxyethanol/water, 8/2, v/v, P(CO)=0.9 atm, at 100°C.     

Convenient synthesis of 3-methyl-1-(4-pyridinyl)-2-butanone using phenyllithium as a metalating agent

3-Methyl-1-(4-pyridinyl)-2-butanone has been synthesized via a short and convenient method based upon acylation of 4-picoline by phenyllithium followed by reaction with ethyl isobutyrate. This procedure can be extended to the preparation of various alkyl pyridyl ketones, intermediates in the synthesis of potential anti-tumor 6-substituted 7H-pyridocarbazole dimers.     

Crystal structures of [Ru(terpy)(HPB)(H2O)](PF6)2 and [Ru(terpy)(HPB)(2-picoline)](PF6) and the kinetics studies of the aqua ligand substitution by pyridine and substituted pyridines

The crystal structures of [Ru(terpy)(HPB)(H₂O)](PF₆)₂, 1, and [Ru(terpy)(HPB)(2-picoline)](PF₆), 2, (where terpy = 2,2′:6′,2′′-terpyridine and HPB = 2-(2′-hydroxyphenyl)-benzoxazole) have been determined. Both structures show slightly distorted octahedral coordination around the ruthenium center. In complex 1, the imine nitrogen of the HPB ligand occupies an axial position and is trans to the aqua ligand whereas in complex 2, the imine nitrogen is trans to the nitrogen of the 2-picoline ligand. The Ru-N(2-picoline) bond distance is much longer than the other Ru-N bonds in the complex due to steric effects from the methyl group of 2-picoline. In both complexes, the phenolate oxygen of the HPB ligand is in the equatorial position and trans to the center nitrogen of the terpyridine. The reaction of [Ru(terpy)(HPB)(H₂O)](PF₆)2 with pyridine and its analogs, 2-picoline and 4-picoline in dichloromethane was monitored spectrophotometrically. There is an initial reduction of the [Ru(III)-H₂O] complex to [Ru(II)-H₂O] complex prior to the substitution of the aqua ligand. The values of the activation parameters indicate that the substitution of the aqua ligand by pyridine, 2-picoline and 4-picoline follow an associative mechanism.     

Transesterification over various zeolites under liquid-phase conditions

Transesterification of β-keto esters with a variety of alcohols to the corresponding β-keto esters has been carried out efficiently over aluminosilicates simply by refluxing in toluene under liquid-phase conditions. Aliphatic β-keto esters exhibit the higher reactivity than the aromatic and/or cyclic β-keto esters, whereas other esters such as -keto esters, ,β-unsaturated esters, normal esters, and -halo esters fail to undergo the transesterification. The reaction proceeds smoothly with primary alcohols than the tertiary-, cyclic-, and allylic alcohols. The large-pore zeolites such as Y, mordenite, and β show higher activity than the medium-pore ZSM-5 and the partial removal of framework aluminum from the large-pore zeolites by dealumination increases their activity. The aluminum containing mesoporous MCM-41 shows poor activity. Among the different solvents used toluene leads to the highest activity and the optimum catalyst concentration found was ca. 20 wt.% of the substrate. The activity increases with increasing reaction temperature. The reaction pathway consists of formation of acyl ketene intermediate by the interaction of β-keto esters with Brønsted acid sites of the catalyst, followed by nucleophilic attack of the alcohol at the electrophilic center and successive elimination of the proton to give the product.     

Effect Factors in Synthesis of Nicotinic Acid by Electrooxidation of 3-Picoline

IntroductionNicotinic acid,whose IUPAC name is3-pyridineformic acid,also called Vitamin B3,is an importantraw material of chemical industry,an intermediate inthe synthesis processes of medicine,additives of food,drink and feed.It is also applied to anti-oxidants in ac-tive dyestuff and household chemicals,such as hair dyeand hair tonic agents,plastic stabilizer and photo-sen-sitive materials,etc.[1—3].There are a fewmethods forsynthesizing nicotinic acid at present.The oxidation of3-picoli…     

Theoretical study of the features of the nuclear-chemical synthesis of phenyl-substituted picoline derivatives

Sections of potential energy surfaces (PES) of phenyl cation addition to picolines were constructed using the DFT/B3LYP and MRCI methods. In the framework of the SA-MCSCF method energies of excited states of the products and intermediates in the reaction of phenyl cation with 4-picoline were determined. The equilibrium geometry and the dissociation energy of intermolecular complexes of benzene and picolines were calculated by the DFT/B3LYP method. The experimentally observed decrease in the yield in the reaction of phenyl cation addition to the 4-picoline as compared with 2- and 3-picolines was substantiated.     

2-甲基吡啶的槽内式间接电氧化

在质子交换膜为隔膜的电解槽内, 以2-甲基吡啶为原料, 以Cr2O72-/Cr3+为媒质, 采用间接电氧化法研究了合成2-吡啶甲酸的反应条件. 实验结果表明, 硫酸浓度、硫酸铬浓度、 反应温度、2-甲基吡啶浓度和阳极电位对产率、转化率、 选择性和电流效率均有影响. 通过变化规律的研究, 找到了各个影响因素的最佳条件为: 硫酸浓度为6.0 mol/L, 反应温度为60 ℃, 硫酸铬浓度为0.15 mol/L, 2-甲基吡啶浓度为0.1 mol/L, 阳极电位为1.50 V.     

A One-Pot Synthesis of 3-Nitro-and 3,5-Dinitro-2-Picolines

3-Nitro- and 3,5-dinitro-2-picoline were each prepared in a one-pot synthesis in high yield by treatment of the respective 2-chloro- 3-nitro- and 2-chloro-3,5-dinitropyridines with diethyl sodiomalonate, followed by hydrolysis and decarboxylation with 50% sulfuric acid.     

Synthesis of 2-arylacrylic esters from aryl methyl ketones via Wittig reaction/singlet oxygen ene reaction

An efficient synthetic method has been developed for the synthesis of 2-arylacrylic esters from the corresponding aryl methyl ketones via Wittig reaction and singlet oxygen ene reaction. Wittig reaction to aryl methyl ketones with (methoxymethyl)triphenylphosphonium chloride in basic condition afforded the methyl enol ethers, and then 2-arylacrylic esters were obtained by singlet oxygen ene reaction, followed by tosylation and elimination in one-pot to the methyl enol ethers in good yields.     

Facile preparation of aromatic esters from aromatic bromides with ethyl formate or DMF and molecular iodine via aryllithium

Various aromatic bromides were treated with n-BuLi and subsequently with ethyl formate, followed by the reaction with ethanol and molecular iodine in the presence of K₂CO₃ to provide the corresponding aromatic ethyl esters in good yields. Moreover, aromatic bromides could be transformed into the corresponding aromatic methyl esters in good yields by the treatment with n-BuLi and subsequently with DMF, followed by the reaction with methanol, molecular iodine, and K₂CO₃. Some aromatics could be also converted into the corresponding aromatic esters in good yields by the treatment with n-BuLi, and subsequently with ethyl formate or DMF, followed by the reaction with molecular iodine and K₂CO₃. The present reactions offer a novel route for the transition-metal-free, carbon-monoxide-free, and therefore environmentally benign one-pot conversion of aromatic bromides and aromatics into aromatic esters.