Regioselective hydroboration-oxidation and -amination of fluoro-substituted styrenes

Hydroboration of fluorinated styrenes with common hydroborating agents results in polymerization. However, regioselective hydroboration has been achieved by utilizing iodoborane-dimethyl sulfide. A series of fluorinated β-phenethyl alcohols and amines were synthesized via this methodology.     

Hydrocarbon acidities calculated with MINDO/3, MNDO,and AM1

Acidities of 32 hydrocarbons have been calculated using MINDO/3, MNDO, and AM1. All three semiempirical procedures have systematic errors and reproduce experimental acidities poorly. A linear correlation, however, does exist between the calculated and experimental results. Correction of the AM1 or MNDO acidities leads to good agreement with literature values even for acids, such as methane and ethylene, whose conjugate bases are small localized anions. Predictions for several hydrocarbons are given.     

硝酸酯化合物生成热的分子轨道研究

用MINDO/3, MNDO和AM1三种SCF-MO方法, 在全优化分子几何构型的基础上, 系统地计算研究了32个硝酸酯化合物的生成热, 与实验值相比, MNDO计算结果偏大很多; MINDO/3计算值与凝聚相实验值符合较好, 由于克服了MNDO法过高地估算原子之间Van der Waals核排斥能的缺点, AM1法给出了较满意的结果: 与七个气态实验值之间存在良好的线性关系(相关系数为0.992), 其间的平均绝对差值和平均差值分别只有10.28和-1.01kJ/mol。     

9-Borabicyclo[3.3.2]decanes and the asymmetric hydroboration of 1,1-disubstituted alkenes

The syntheses of the optically pure asymmetric hydroborating agents 1 (a, R = Ph; b, R = TMS) in both enantiomeric forms are reported. These reagents are effective for the hydroboration of cis-, trans- and trisubstituted alkenes. More significantly, they exhibit unprecedented levels of selectivity in the asymmetric hydroboration of 1,1-disubstituted alkenes (28-92% ee), a previously unanswered challenge in the nearly 50 year history of this reagent-controlled process. For example, the hydroboration of alpha-methylstyrene with 1a produces the corresponding alcohol 6f in 78% ee (cf., Ipc2BH, 5% ee). Suzuki coupling of the intermediate adducts 5 produces the nonracemic products 7 very effectively (50-84%) without loss of optical purity.     

Enthalpy of formation of thiophene derivatives

The enthalpy of formation in the gas phase has been calculated for 21 carbonyl compounds of the thiophene series with the aid of the PM3, MINDO, AM1, and MNDO semiempirical quantum-chemical methods. Comparison of them with experimental data showed that the best linear correlation was achieved with the PM3 method. The latter in conjunction with a developed linear regression equation has been used to predict the enthalpy of formation of 22 carboxylic acids and ketones of the thiophene series.     

丙二酰氧基硼氢化钠与烯烃的选择性硼氢化

叙述了丙二酰氧基硼氢化钠的制备及其原位与烯烃的选择性硼氢化反应。通过化学反应证实,丙二酰氧基硼氢化钠在THF中与脂肪族末端烯烃例如1-庚烯的硼氢化反应,有98%的硼原子加到双键末端碳原子上,只有2%的硼原子加到2-位上,生成单取代的有机硼化合物,即丙二酰氧基硼氢化钠是一个单官能硼氢化试剂。     

Hydroboration with pyridine borane at room temperature

Treatment of pyridine borane (Py.BH3) with iodine, bromine, or strong acids affords activated Py.BH2X complexes that are capable of hydroborating alkenes at room temperature. Evidence is presented for an unusual hydroboration mechanism involving leaving group displacement. In contrast to THF.BH3, hydroboration with Py.BH2I selectively affords the monoadducts. The crude hydroboration products are converted into synthetically useful potassium alkyltrifluoroborate salts upon treatment with methanolic KHF2.     

Scope of the Suzuki-Miyaura aminoethylation reaction using organotrifluoroborates

Potassium beta-aminoethyltrifluoroborates were prepared in good yields via hydroboration of the corresponding enecarbamates using the Snieckus hydroborating reagent. A wide variety of phenethylamines containing a potentially free primary amine after appropriate deprotection have been successfully prepared in good yield using these organotrifluoroborates as partners in Suzuki-Miyaura coupling with aryl bromides, iodides, and triflates.     

In quest of factors that control the enantioselective catalytic Markovnikov hydroboration/oxidation of vinylarenes

This study attempts to rationalise the unpredictable performance of transition metal catalysed asymmetric hydroboration of vinylarenes on varying the precursor of the catalyst from cationic to neutral species, [M(cod)(L-L)]BF4, [M(mu-Cl)(cod)]2/(L-L), the metal (M=Rh and Ir), and the hydroborating reagent (catecholborane, pinacolborane). The approaches are based on the agreement between experimental data provided by (R)-Binap and (R)-Quinap modified catalytic systems and computational data evidenced by DFT calculations and QM/MM strategies. Unprecedentedly high enantiomeric excesses in the hydroboration/oxidation of vinylarenes with both electron-withdrawing substituents ((R)-(+)-1-p-F-phenylethanol, ee up to 92 %) and electron-releasing substituents ((R)-(+)-1-p-MeO-phenylethanol, ee up to 98 %), can be attributed to a rhodium halide key intermediate.     

Semiempirical infrared spectra simulations for some aromatic amines of interest for azo dye chemistry.

A set of semiempirical methods (PM3, AM1, MNDO, MNDO3, INDO, CNDO and ZINDO/1) has been tested to find the best tool for the identification of aromatic amines by infrared spectroscopy. Analysed were 1,4-, 1,3-, 1,2-phenylenediamines and aniline, amines commonly used in the dye industry. Of all the semiempirical methods tested, AM1 showed the closest correspondence to experimental values. It provided the best linearity between the calculated and experimental frequencies (correlation coefficient, cc = 0.9993). In the range of -NH2 stretching vibrations, the best correspondence between the theoretical and experimental frequencies was achieved for the PM3 method (cc = 0.8369).     

MNDO study of reaction paths: Hydroboration of carbonyl systems

The hydroboration reactions of acetaldehyde and acetone have been investigated by the MNDO method. The reactions have been shown to be twostep reactions involving an intermediate adduct. This adduct subsequently undergoes hydrogen rearrangement. The hydroboration reactions of acetaldehyde and acetone have been compared with the corresponding reaction of formaldehyde. The charge transfer effects accompanying these reactions have also been discussed.     

Enthalpy of formation of adamantane alkyl derivatives

The enthalpies of formation of adamantane alkyl derivatives were calculated by the semiempirical quantum chemical methods PM3, MINDO, AM1 and MNDO of the MOPAC software package. Comparison of the calculated values with the experimental data showed that the best correlation gave the PM3 method. Using this method and linear regression equation derived by us we calculated enthalpies of formation of twenty-two alkyl derivatives of adamantane.     

MNDO study of reaction paths: Hydroboration of methyl cyanide

The hydroboration reaction of methyl cyanide has been investigated by the MNDO method. It has been shown that the reaction requires an activation energy of 25.3 kcal/mol and involves a four-center-like transition state in the rate-determining step. This reaction has been compared with the corresponding reaction of hydrogen cyanide, and the effect of methyl substitution on the reaction has been discussed. The charge-transfer effects accompanying the reaction have also been studied.     

PM3, AM1, MINDO3 semi-empirical IR spectra simulations for some nitriles of interest for Titan's chemistry

A set of the semi-empirical methods (PM3, AM1, MNDO and MINDO3) has been tested to find the best auxiliary tool for the identification of nitriles by gas chromatography/Fourier transform IR spectroscopy/mass spectrometry, considering five nitriles of interest for Titan's chemistry as test compounds: acetonitrile, acrylonitrile, cyanoacetylene, 2-butynenitrile and dicyanoacetylene. Of the four semi-empirical methods, MNDO can be considered as the most advantageous auxiliary tool for the gas chromatography/Fourier transform IR spectroscopy/mass spectrometry (GC/FTIR/MS) identification of nitriles of interest for Titan's atmospheric chemistry, since (1) the simulated IR spectra best match the experimental (in some cases AM1 gives comparable results); (2) it provides the best linearity between the calculated and experimental frequencies (correlation coefficient of 0.990); a scaling factor of 0.90 can be applied to afford better correspondence between the calculated and experimental wavenumbers. At the same time, none of the methods is able to predict infrared intensities and a spectral intensity pattern.     

Organoboranes for synthesis. 4 : Oxidation of organoboranes with pyridinium chlorochromate. A direct synthesis of aldehydes from terminal alkenes via hydroboration

The oxidation of trialkylboranes containing primary a1kyl groups with pyridinium chlorochromate (PCC) in methylene chloride provides the corresponding aldehydes in good yields. The stoichiometry for the oxidation of alcohols, borate esters and trialkylboranes with PCC has been examined. In view of the poor regioselectivity (only 94% primary alkyl groups) and functional group tolerance observed in the hydroboration with borane (BH₃.THF or BH₃.SMe₂), a more selective hydroborating agent, bis(3-methyl-2-butyl)borane (disiamylborane), was utilized for the preparation of aldehydes from terminal alkenes. However, the formation of 3-methyl-2-butanone as a by-product, and the requirement of six moles of PCC per mole of aldehyde are major disadvantages in this method. This difficulty was circumvented by employing monochloroborane-dimethyl sulfide for hydroboration. This reagent exhibits high regioselectivity (⪢ 99% primary alkyl groups) in the hydroboration of terminal alkenes. Oxidation of the resulting dialkylchloroborane following hydrolysis affords the desired aldehydes in satisfactory yields. Consequently, the hydroboration of terminal alkenes, followed by PCC oxidation, represents a direct convenient method for the transformation of alkenes into the corresponding aldehydes.     

A CNDO/S study on the alkylbenzene-TCNE complexes

The calculations based on the semiempirical CNDO/S Hamiltonian appeared useful in predicting the electronic structures of electron donor-acceptor (EDA) complexes of tetracyanoethylene (TCNE) and various alkylbenzenes. The results are in satisfactory agreement with the experimental data. The calculated complex stabilization energies are related to the experimental gas phase enthalpies of formation by linear regression (τ = 0.941). A fairly good correlation (τ = 0.985) between the measured and calculated energies of the charge transfer (CT) electronic transitions is established. The problem of double CT absorption bands is discussed by referring to the theoretical results. The ionization potentials of alkylbenzenes calculated by CNDO/S and MNDO methods are considered as well.     

Enthalpies of formation of nitro-, nitroxy-, and nitrosoadamantanes

The enthalpies of formation of nitro-, nitroso-, and nitroxyadamantanes were calculated using semiempirical quantum-chemical PM3, MINDO, AM1, and MNDO methods incorporated into MOPAC software package. The best correlation with the experimental data was obtained with the results of PM3 calculations. Using the corresponding linear regression equation, the enthalpies of formation of 22 adamantane derivatives having nitro-, nitroso-, and nitroxy groups were calculated.     

Dependence of the reactivity of five-membered heterocycles on their structure. 3. Proton affinity of azoles and oxazoles

The proton affinity (PA) of a number of azoles and oxazoles was calculated by MNDO and STO-3G ab initio methods. In spite of the fact that these methods predict poorly the absolute values of the PA, a good correlation between the PA values calculated by STO-3G and the experimental values of PA as well as pK_a values exists. Correlation of the experimental values with MNDO results are much worse.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 508–511, April, 1989.     

Molten salts bearing anion receptor

A series of organoboron molten salts prepared by hydroboration of allyl imidazolium type molten salts with various hydroborating reagents such as monobromoborane dimethyl sulfide complex, 9-borabicyclo[3.3.1]nonane (9-BBN) and mesitylborane, and subsequent anion exchange reaction exhibited selective cation transporting property with ionic conductivity of 7.79 x 10(-5) - 6.25 x 10(-6) S cm(-1) at 323 K.     

Comparative semiempirical calculations of tetrazole derivatives

Heats of formation, protonation energies, charge distributions, dipole moments, and geometrical structures of thirty-two 1-, 2-, 1,5-, and 2,5-substituted tetrazoles have been investigated by different semiempirical SCF MO calculations. MNDO and, in some cases, AM 1 methods are the most acceptable for tetrazole derivatives. A number of linear correlations between available experimental data and the calculated energies and charge characteristics have been established. © 1992 John Wiley & Sons, Inc.