Quantum-Chemical Investigation of the Electronic and Spatial Structure of 1-Vinyltetrazoles

Calculations have been carried out of the total Mulliken charges on carbon and nitrogen atoms, the relative stability, and equilibrium populations of the s-cis(R) and s-trans(R) conformers of a series of 1-vinyl-5R-tetrazoles (R = H, Me, n-Bu, tert-Bu, Ph, NH₂, I, CF₃, NO₂) by the ab initio MP2/6-31G** method. Out-of-plane structures correspond to the stable s-cis(R) conformer, and the deviation from planarity grows regularly with an increase in the bulk of the substituent. The proportion of s-trans(R) conformation increases in the same series and reaches 100% for R = tert-C₄H₉. The data of quantum-chemical calculations are in agreement with the results of investigations of the spatial structure of 1-vinyl-5R-tetrazoles by ¹H and ¹³C NMR methods. Values of the total energies of the corresponding homodesmotic reactions were calculated to assess the effect of the nature of the substituent in position 5 of the tetrazole ring on the size of the conjugation energy in planar s-trans(R) conformations of the compounds investigated. The quantum-chemical calculations carried out show that the conjugation energy decreases regularly according to the increase in electron-withdrawing properties of the substituent in position 5 of the ring.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 537–548, April, 2005.     

Réactivité des diénamines épiconjuguées des Δ3(9) hydrindénones—4V : Stéréochimie de la formation des δ-dicétones et de diverses attaques électrophiles

The cross-conjugated dienamines of Δ4 4-hydrindenones react with methylvinylketone (or other electrophilic reagents such as H⁺, I CH₃) at the face opposite to their angular substituent at R(8). The axial attack, in the case of methylvinylketone,. leads to the isomer of the δ-diketone in which the bulky oxo-3 butyl-1 group is in an axial position. The thermodynamic equilibrium shows that this isomer is the less stable one. Therefore, kinetic control of the reaction is a steric approach control. The high degree of stereoselectivity of the reaction depends both upon the nature of the substituent R(8) = H or CH₃ and the nature of the electrophilic reagent.     

Arbuzov rearrangement in the 1,3,2-oxazaphosphinane series

Reactions of 2-alkoxy-1,3,2-oxazaphosphinanes (including 3-alkyl derivatives) with methyl and ethyl bromoacetates give two types of Arbuzov rearrangement products (cyclic and acyclic ones). The ratio between their yields is virtually independent of the nature of the substituent in position 3 of the starting reagent, being mainly determined by the nature of the substituent in the phosphorus bound alkoxy group and varying from 96 : 4 to 2 : 98. Acyclic products can be converted into cyclic ones.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1915–1918, September, 2004.     

Hydroformylation of 1-octene in the presence of cobalt alkylidynecarbonyl clusters

The hydroformylation of 1-octene in the presence of Co₃(CO)₉(-CR) (R=H, Me, Ph, CO₂Me, CO₂Et, CO₂Prⁱ, CO₂Bu^t, Cl, Br, OMe) alkylidynecarbonyl clusters, as well as triphenylphosphine derivatives of these complexes and heteronuclear Co₂Ni compounds have been studied. The nature of the catalytically active species in hydroformylation, as well as the processes of their formation and transformation during the reaction, have been established by means of IR spectroscopy. The effects of the reaction conditions, the nature of the substituent at the apical carbon atom, the electron donating phosphine substituent, and the substituent in the metal cluster framework have been discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1388–1393, August, 1993.     

Kinetics of hydrolysis of some new heterocyclic azomethines

Kinetics of base hydrolysis of new heterocyclic azomethines derived from active methyl quaternary salts and aromatic nitroso compounds were investigated in the presence of 70% (wt/wt) water-methanol. The base hydrolysis of these compounds is strictly first-order with respect to OH^– and azomethine. The rate determining step is suggested to be the attack of the hydroxide ion on the free base. Effects of water content and nature of organic hydroxylic solvent have been studied. It is concluded that specific solute-solvent interactions through dispersion forces play a major role in the base hydrolysis rate of the azomethines investigated. The effect of pH (2.98 – 12.24) on hydrolysis rates of compounds having a diethylamino substituent in the presence of 30% methanol has been studied. In acidic media, the rate determining step is probably the water attack on the protonated substrate.     

取代基对有机铬化合物分子内氢转移反应势垒的影响

使用密度泛函理论B3LYP方法研究了取代基对一系列有机Cr化合物(R₃)(R₄)Cr(≡CH)(CHR₁R₂)分子内α-H转移反应能垒的影响。确定了反应物、过渡态和产物的几何结构和反应势垒。研究结果表明,当R₁和R₂是甲基,R₃和R₄是PH₂基团、Silyl基团或Cl原子时,反应势垒最低。     

Alkyl alkynylphosphonites in the Kabachnik-Fields reaction

O-Ethyl alkynylphosphonites [EtOP(O)(H)CэCR] (1 and2) react withp-bromobenzaldehyde and benzylamine to form the usual acyclic products of the Kabachnik-Fields reaction or phosphorus-containing heterocycles depending on the nature of the substituent R at the β-carbon atom of the acetylene fragment of phosphonite. In the case of R=Bu^t,O-ethyl (α-benzylamino-p-bromobenzyl)(3,3-dimethylbut-1-ynyl)phosphinate (3) was obtained. In the case of R=Me, 1-benzyl-2-p-bromophenyl-3-ethoxy-5-methyl-3-oxo-Δ⁴-1,3-λ⁵-azaphospholine (4) was formed. Compounds3 and4 were also synthesized by the reactions of the above-mentioned phosphonites with the corresponding azomethines. Dedicated to the memory of Academician M. I. Kabachnik on his 90th birthday. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2104–2106, October, 1998.     

Reaction of methyl iodide with organylethynyl silatranylmethyl chalcogenides

The reactivity of organylethynyl silatranylmethyl chalcogenides RC=CYCH₂Si(OCH₂CH₂)₃N (R=Ph, Me₃Si; Y=S, Se, Te) in the reaction with methyl iodide depending on the nature of the chalcogen Y, the substituent R at the triple bond, and the reaction conditions was studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2550–2551, December, 1998.     

Reaction of Tertiary 2-Chloroketones with Cyanide Ions: Application to 3-Chloroquinolinediones

3-Chloroquinoline-2,4-diones react with cyanide ions in dimethyl formamide to give 3-cyanoquinoline-2,4-diones in small yields due to the strong hindrance of the substituent at the C-3 atom. Good yields can be achieved if the substituent at this position is the methyl group. In the methanol solution, the reaction proceeds by an addition mechanism to form 2-oxo-1a,2,3,7b-tetrahydrooxireno[2,3-c]quinoline-7b-carbonitriles, from which 4-hydroxy-3-methoxy-2-oxo-1,2,3,4-tetrahydroquinoline-4-carbonitriles are subsequently formed by opening of the epoxide ring with methanol. Some minor products of these reactions have also been isolated. The ¹H, ¹³C and ¹⁵N NMR spectra of the prepared compounds were measured, and all resonances were assigned using appropriate two-dimensional spectra.     

Reaction of Pyridoxal with Hydrophosphoryl Compounds

The products of carbonyl phosphonylation of pyridoxal with dialkylphosphinous acid, alkylphosphinic acid ethyl esters, and phosphorous acid dialkyl (or diphenyl) esters have been obtained for the first time. In some cases, the products of addition are hydrolytically unstable and stabilized by forming internal betaine structures. The reaction of pyridoxal with phosphorous acid in alcohol solutions gives alkoxyfuropyridines possessing the iminium nitrogen atom. The structure and composition of the prepared compounds have been established by ³¹P and ¹H NMR spectroscopy, mass spectrometry (MALDI‐TOF), and X‐ray analysis.     

A 13C n.m.r. study of the B6 vitamins and of their aldimine derivatives

The vitamins, pyridoxine, pyridoxal, pyridoxamine, pyridoxal-5′-phosphate and pyridoxamine-5′-phosphate, have been studied in aqueous solution over a pH range of 2–12 by ¹³C nuclear magnetic resonance spectroscopy. Resonance assignments are made primarily by the spin–spin coupling constants of carbons with protons and with phosphorus. The proton–carbon coupling constants show a marked conformational dependence in the hemiacetal form of pyridoxal. Furthermore, the H-6? C-5 coupling constant in the vitamins is much smaller than the corresponding constant in pyridine. This may be due either to an effect of the C-5 substituent in vitamins or to a different electronic configuration of the zwitterionic hydroxypyridine ring. The addition of manganese to a solution of pyridoxal phosphate causes line broadenings consistent with the interaction of the metal ion with this vitamin at the formyl and phenolic oxygens. The chemical shifts of the aromatic carbons of pyridoxine have been calculated, as a function of pH, by summing shielding parameters which were estimated empirically from pyridine derivatives. The calculated shifts agree well with the experimental data for C-3, C-5 and C-6, less well for C-2, and poorly for C-4. The deviation from additivity for C-4 indicates a preferred orientation for the 4-hydroxymethyl substituent caused by internal hydrogen bonding between the substituents at C-3 and C-4. Evidence is presented for the existence of the free aldehyde form of pyridoxal at alkaline pH. Aldimine complexes of pyridoxal and pyridoxal phosphate with amines and amino acids have also been studied. Characteristic chemical shift changes caused by both pyridinium and aldimine nitrogen deprotonations are seen. Additionally, the chemical shifts of carbons of the pyridine ring are dependent upon the structure of the imine, especially when the aldimine nitrogen is protonated. We conclude that this dependency is due to steric effects in an aldimine complex which is constrained by internal hydrogen bonding. We also discuss the merits of carbons 3 and 4 as possible sites of cofactor labeling for enzymatic studies.     

Relative reactivity of substituted acetophenones in enantioselective biocatalytic reduction catalyzed by plant cells of Daucus carota and Petroselinum crispum

We have examined enantioselective bioreduction of acetophenone and its substituted derivatives into corresponding S-alcohols catalyzed by Daucus carota and Petroselinum crispum plant cells in water and isooctane. We found that the nature of the substituent has a profound effect on the relative reactivity of substituted acetophenones and enantioselectivity of biocatalytic reduction. Electron-withdrawing substituents –Br and –NO₂ enhance the initial rate of reaction and yields of products, while electron-donating substituent –OCH₃ decreases them. The reduction rates and yields of products in water were noticeably higher in comparison with similar reductions conducted in isooctane. Correlations between the initial reaction rate and the substituent constant (σ⁺) in the aromatic ring characterizing its nature were established. Comparison of ρ constants of bioreduction catalyzed by D. carota and P. crispum shows that the sensitivity of the reduction to the nature of the substituents is more significant in the case of D. carota biocatalyst. Comparison of ρ constants for D. сarota and P. crispum in water and isooctane indicates that the sensitivity of bioreduction to the nature of the substituent tends to increase from water to isooctane.     

Structures and conformations of 1-aryl-1,4-dihydro-3(2H)-isoquinolinones

The X-ray crystal structures of series of 1-aryl-1,4-dihydro-3(2H)-isoquinolinones (1-7) have been determined. Lactame heterocyclic ring possesses more or less deformed boat conformation in all examined structures. The aryl substituent adopts the equatorial position in the structures 1-3 and the axial one in 5-7. In the structure of 4, due to extremely flattened heterocyclic ring, aryl substituent location can be named as bisectional. In all solved structures the molecules are joined into the dimers via two N-H?O hydrogen bonds. At the same time, ¹H NMR studies in DMSO-d₆ solutions were accomplished and profound analysis of ²J, ³J, and ⁵J coupling constants have shown that in isoquinolinone system the heterocyclic ring adopts the boat conformation in all investigated compounds. The stereochemical orientations of the phenyl ring at C1 do not depend on the nature of the substituent but, exclusively, on the mode of substitution. However, three forms of undulated laktam heterocyclic ring conformation in respect of 1-aryl substituent positions were confirmed by calculation (conformational analysis).     

Polymerization of epoxidized triglycerides with fluorosulfonic acid

The use of triglycerides as agri-based renewable raw materials for the development of new products is highly desirable in view of uncertain future petroleum prices. A new method of polymerizing epoxidized soybean oil has been devised with the use of fluorosulfonic acid. Depending on the reaction conditions, one can get a viscous oil or a solid as the reaction product. The reaction mechanism has been studied through a systematic examination of the fluorosulfonic acid-initiated reaction of epoxidized methyl oleate and epoxidized methyl linoleate. Through ¹³C NMR spectroscopy, the major species derived from fluorosulfonic acid-initiated polymerization of epoxidized soybean oil have been determined. The effects of temperature, initiator dosage, and reaction time have been studied and shown to affect the nature of polymer products obtained and the distribution of different chemical species present.     

On the regioselectivity of the intramolecular [2 + 2]-photocycloaddition of alk-3-enyl tetronates

The simple diastereoselectivity and the regioselectivity of the [2 + 2]-photocycloaddition of alk-3-enyl tetronates were studied, depending on the nature of the substituent R in the α-position. Fourteen tetronates were synthesized and their intramolecular photocycloaddition reactions performed. If R was an alkoxycarbonyl group and if the olefin, which underwent the intramolecular addition, was sterically congested, crossed photoproducts prevailed and were formed in yields between 35 and 65%. In all other cases, the straight photoproducts were obtained as the main reaction products in yields ranging from 39 to 84%. The structures of the photochemical products were thoroughly investigated by one- and two-dimensional NMR experiments. In all cases, the diastereoselectivitiy was excellent and only a single diastereoisomer was formed. A mechanistic model is proposed, which explains the regioselectivity of the [2 + 2]-photocycloaddition reaction.     

Quantum-chemical calculations of O-O bond strengths in organic hydrotrioxides

The O-O bond strengths in ten organic hydrotrioxides have been calculated by semiempirical MNDO and AMI methods. The RO-OOH bond strength is independent of the nature of substituent R and is equal to 20.4±1.1 kcal mol^–1 (AM1). The influence of the inductive effect of substituent R on the value ofD(ROO-OH) has been established.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1129–1131, May, 1996.     

Synthesis and isomerism of 2-(3,5-diaryl-1H-pyrazol-4-yl)-1H-benzimidazoles

2-(3,5-Diaryl-1H-pyrazol-4-yl)-1H-benzimidazoles have been obtained by the cyclocondensation of 2-phenacyl-1H-benzimidazoles with 4-nitro- and 4-methoxybenzoylhydrazines. The reaction mechanism and the isomerism of the obtained products are discussed. According to the data of ¹H NMR spectroscopy the stabilized isomer is that in which the electron-withdrawing aryl substituent is located in position 3 and the electron-donating substituent in position 5 of the pyrazole ring.