Total synthesis of the Amaryllidaceae alkaloid clivonine

Two syntheses of the Amaryllidaceae alkaloid clivonine (1) are described. Both employ previously reported 7-arylhydrindane 6 as an intermediate but differ in the method employed for subsequent introduction of what becomes the ring-B lactone carbonyl carbon (C7). The synthesis featuring a Bischler-Napieralski reaction for this transformation constitutes the first asymmetric synthesis of natural (+)-clivonine. Crystal structures for compounds (±)-13, (±)-16, (-)-20 and (±)-28 are also reported.     

A kinetic study of rearrangement and degradation reactions of tetrathionate and trithionate in near-neutral solutions

The kinetics of reactions of trithionate and tetrathionate via different reaction pathways were studied in near-neutral solutions. In the case of trithionate, the predominant degradation reaction is hydrolysis to thiosulfate and sulfate. The pseudofirst-order rate constant is independent of pH and measured to be (6.2 ± 0.2) × 10(-7) s(-1) for the pH range of 5.5-10.5. With tetrathionate, the reaction in both neutral and alkaline solutions occurs via a thiosulfate catalyzed rearrangement reaction to trithionate and pentathionate followed by their further reactions. The data suggest that when thiosulfate is completely absent, this first step will not occur, and in the presence of thiosulfate, the rate of the first step is independent of pH in the pH range 6-8. The secondary reactions include the hydrolysis of trithionate and the further rearrangement and degradation of pentathionate. This mechanism explains the dominant reaction products for both neutral and alkaline solutions. In the presence of thiosulfate and at near-neutral pH, the rearrangement reactions dominate over the degradation reactions and exhibit second-order kinetics, with the rate constants in the pH range of 6-8 determined to be (4.24 ± 0.26) and (1.89 ± 0.18) × 10(-4) M(-1) s(-1) for tetra- and pentathionates, respectively. At extremely low thiosulfate concentrations, the main secondary reaction is the hydrolysis of trithionate at pH < 7, and at pH > 7, the degradation of pentathionate.     

Nitrosation, thiols, and hemoglobin: energetics and kinetics

Nitrosothiols are powerful vasodilators. Although the mechanism of their formation near neutral pH is an area of intense research, neither the energetics nor the kinetics of this reaction or of subsequent reactions have been addressed. The following considerations may help to guide experiments. (1) The standard Gibbs energy for the homolysis reaction RSNO → RS(?) + NO(?)(aq) is +110 ± 5 kJ mol(-1). (2) The electrode potential of the RSNO, H(+)/RSH, NO(?)(aq) couple is -0.20 ± 0.06 V at pH 7. (3) Thiol nitrosation by NO(2)(-) is favorable by 37 ± 5 kJ mol(-1) at pH 7. (4) N(2)O(3) is not involved in in vivo nitrosation mechanisms for thermodynamic--its formation from NO(2)(-) costs 59 kJ mol(-1)--or kinetic--the reaction being second-order in NO(2)(-)--reasons. (5) Hemoglobin (Hb) cannot catalyze formation of N(2)O(3), be it via the intermediacy of the reaction of Hb[FeNO(2)](2+) with NO(?) (+81 kJ mol(-1)) or reaction of Hb[FeNO](3+) with NO(2)(-) (+88 kJ mol(-1)). (6) Energetically and kinetically viable are nitrosations that involve HNO(2) or NO(?) in the presence of an electron acceptor with an electrode potential higher than -0.20 V. These considerations are derived from existing thermochemical and kinetics data.     

Kinetics and mechanism of hydrogen-atom abstraction from rhodium hydrides by alkyl radicals in aqueous solutions

The kinetics of the reaction of benzyl radicals with [L(1)(H(2)O)RhH{D}](2+) (L(1)=1,4,8,11-tetraazacyclotetradecane) were studied directly by laser-flash photolysis. The rate constants for the two isotopologues, k=(9.3±0.6) × 10(7) M(-1) s(-1) (H) and (6.2±0.3) × 10(7) M(-1) s(-1) (D), lead to a kinetic isotope effect k(H)/k(D)=1.5±0.1. The same value was obtained from the relative yields of PhCH(3) and PhCH(2)D in a reaction of benzyl radicals with a mixture of rhodium hydride and deuteride. Similarly, the reaction of methyl radicals with {[L(1)(H(2)O)RhH](2+) + [L(1)(H(2)O)RhD](2+)} produced a mixture of CH(4) and CH(3)D that yielded k(H)/k(D)=1.42±0.07. The observed small normal isotope effects in both reactions are consistent with reduced sensitivity to isotopic substitution in very fast hydrogen-atom abstraction reactions. These data disprove a literature report claiming much slower kinetics and an inverse kinetic isotope effect for the reaction of methyl radicals with hydrides of L(1)Rh.     

Acid-promoted rearrangement of drimane type epoxy compounds and their application in natural product synthesis

The reactions of (±)-α-epoxy drimenol (4) and (±)-α-epoxy drimenyl cyanide (6) with acids (proton acid or Lewis acid) selectively gave the rearranged aldehyde (±)-13 and (±)-15 having the hydroindane skeleton, respectively, while the reactions of (±)-4 and (±)-6 with Dibal-H selectively afforded the allyl alcohol (±)-14 and (±)-16, respectively. The reactions of (8aR)-6 and (8aS)-6 with Dibal-H were applied for the determination of the absolute structure of natural 7β-acetoxy-ent-labda-8(17),13(14)E-dien-15-ol (18). The reaction of (±)-α-epoxy bicyclofarnesol (5) and (8aS)-5 with proton acid selectively provided the rearranged ketol (±)- and (8aS)-31 having the hydroindane skeleton, respectively. The optically active (8aS)-31 was converted to the natural (9S)-austrodoric acid (33).     

An approach to aliphatic 1,8-stereocontrol: diastereoselective syntheses of (±)-patulolide C and (±)-epipatulolide C

The tin(iv) bromide promoted reaction of 7-hydroxy-7-phenylhept-2-enyl(tributyl)stannane 11 with benzaldehyde gave a mixture of the epimeric 1,8-diphenyloct-3-ene-1,8-diols 12 and so indirect methods were developed for aliphatic 1,8-stereocontrol to complete diastereoselective syntheses of (±)-patulolide C 1 and (±)-epipatulolide C 40. (5Z)-3,7-syn-7-(2-Trimethylsilylethoxy)methoxyocta-1,5-dien-3-ol 17 was prepared from the tin(iv) chloride promoted reaction of 4-(2-trimethylsilylethoxy)methoxypent-2-enyl(tributyl)stannane 16 with acrolein (1,5-syn?:?1,5-anti = 96?:?4). An Ireland-Claisen rearrangement of the corresponding benzoyloxyacetate 21 with in situ esterification of the resulting acid using trimethylsilyldiazomethane gave methyl (4E,7Z)-2,9-anti-2-benzyloxy-9-(2-trimethylsilylethoxy)methoxydeca-4,7-dienoate 22 together with 10-15% of its 2,9-syn-epimer 26, the 2,9-syn-?:?2,9-anti-ratio depending on the conditions used. An 88?:?12 mixture of esters was taken through to the tert-butyldiphenylsilyl ether 38 of (±)-patulolide C 1 together with 6% of its epimer 39, by reduction, a Wittig homologation and deprotection/macrocyclisation. Following separation of the epimeric silyl ethers, deprotection of the major epimer 38 gave (±)-patulolide C 1. The success of 2,3-Wittig rearrangements of allyl ethers prepared from (5Z)-3,7-syn-7-(2-trimethylsilylethoxy)methoxyocta-1,5-dien-3-ol 17 was dependent on the substituents on the allyl ether. Best results were obtained using the pentadienyl ether 56 and the cinnamyl ether 49 that rearranged with >90?:?10 stereoselectivity in favour of (1E,5E,8Z)-3,10-syn-1-phenyl-10-(2-trimethylsilylethoxy)methoxyundeca-1,5,8-trien-3-ol 50. This product was taken through to the separable silyl ethers 38 and 39, ratio 7?:?93 by regioselective epoxidation and alkene reduction using diimide, followed by deoxygenation, ozonolysis, a Wittig homologation and selective deprotection/macrocyclisation. Deprotection of the major epimer 39 gave (±)-epipatulolide C 40.     

Guest binding dynamics with cucurbit[7]uril in the presence of cations

The binding dynamics of R-(+)-2-naphthyl-1-ethylammonium cation (NpH(+)) with cucurbit[7]uril (CB[7]) was investigated. Competitive binding with Na(+) or H(3)O(+) cations enabled the reaction to be slowed down sufficiently for the kinetics to be studied by fluorescence stopped-flow experiments. The binding of two Na(+) cations to CB[7], i.e., CB[7]·Na(+) (K(01) = 130 ± 10 M(-1)) and Na(+)·CB[7]·Na(+) (K(02) = 21 ± 2 M(-1)), was derived from the analysis of binding isotherms and the kinetic studies. NpH(+) binds only to free CB[7] ((1.06 ± 0.05) × 10(7) M(-1)), and the association rate constant of (6.3 ± 0.3) × 10(8) M(-1) s(-1) is 1 order of magnitude lower than that for a diffusion-controlled process and much higher than the association rate constant previously determined for other CB[n] systems. The high equilibrium constant for the NpH(+)@CB[7] complex is a consequence of the slow dissociation rate constant of 55 s(-1). The kinetics results showed that formation of a complex between a positively charged guest with CB[n] can occur at a rate close to the diffusion-controlled limit with no detection of a stable exclusion complex.     

Nucleophilic addition to 2,3-disubstituted butanal derivatives and their application to natural product synthesis

The reaction of 2,3-anti-2-tert-butyldimethylsiloxy-3-substituted butanal derivative [anti-B, (±)-10 and (±)-16] derived from trans-(2,3)-epoxy butanoate (1) with carbon nucleophiles [α-furyl anion, acetate anion, and indium (In)-assisted allyl anion] has been investigated to give selectively the anti-, anti-adduct D. This anti-stereoselection could be explained by the Felkin-Anh transition state model. Thus obtained anti-, anti-adducts (±)-17 and (±)-38 were formally converted to natural products, (±)-asperlin (2) and (±)-olivose (4), respectively. The major anti-, anti-adduct (±)-26 was converted to (±)-digitoxose (3), while the minor anti-, syn-adduct (±)-27 was also converted to (±)-olivose (4). The reaction of (±)-10 with tert-butyl acetate anion gave predominantly afforded the anti-, anti-adduct (±)-23, which was converted to (±)-1,5-dideoxyhexitol (25). Alternately, the reaction of 2,3-syn-2-tert-butyldimethylsiloxy-3-p-methoxyphenoxy butanal derivative [syn-B, (±)-14] derived from trans-(2,3)-epoxy butanoate (1) with carbon nucleophile (In-assisted allyl anion) afforded a ca. 1 : 1 mixture of the syn-, anti-adduct E [(±)-32 or (±)-34] and syn-, syn-adduct F [(±)-33 or (±)-35]. After separation of this mixture, (±)-34 and (±)-35 were separately converted to (±)-oliose (5) and (±)-boivinose (6), respectively.     

Structural and mechanistic information on the nitrosation of model Fe(II) complexes containing a biomimetic S4N chelate

In order to provide insight into the reaction pathways of nitrogen oxide redox species with [Fe-S] models that may parallel those existing in biology, the reactivity of the iron-sulfur species, {[Fe(II)(S(4)NEt(2)N)]}(2) (1) and [Fe(II)(CH(3)CN)(S(4)NEt(2)N)] (2), where (S(4)NEt(2)N)(2-) = 2,6-bis(2-mercaptophenylthiomethyl)-4-diethylaminopyridine(2-), towards NO(+) (nitrosation) has been studied mechanistically in acetonitrile and compared with the corresponding reactions with NO (nitrosylation). For the nitrosation of 1, the reaction takes place in two steps that correspond to the nitrosation of the mononuclear (2) and dinuclear (1) complexes, respectively. For the corresponding carbonyl complex [Fe(II)(CO)(S(4)NEt(2)N)] (3), the nitrosation reaction occurs in a single step. The relative reactivity of the iron-sulfur species is approximately (1)/(2)/(3) = 1/20/10. Activation parameters for the nitrosation of 1 (ΔH(#) = 27 ± 1 kJ mol(-1), ΔS(#) = -111 ± 2 J K(-1) mol(-1), and ΔV(#) = -19 ± 2 cm(3) mol(-1)), 2 (ΔH(#) = 46 ± 2 kJ mol(-1), ΔS(#) = -22 ± 7 J K(-1) mol(-1), and ΔV(#) = -9.7 ± 0.4 cm(3) mol(-1)) and 3 (ΔH(#) = 38 ± 1 kJ mol(-1), ΔS(#) = -44 ± 4 J K(-1) mol(-1), and ΔV(#) = -7.8 ± 0.3 cm(3) mol(-1)) were determined from variable temperature and pressure studies. The significantly negative ΔS(#) and ΔV(#) values found for the nitrosation reactions are consistent with an associative mechanism. A comparative study of the reactivity of the iron-sulfur species 1 to 3 towards NO(+) and NO is presented.     

Hydrolysis Reactions and Resolution of (±)-2-Acetamido-3-hydroxy-1-(4-nitrophenyl)-1-propanone

IntroductionChloramphenicol,which was isolated fromStreptomyces venezuelae in 1 947[1] ,is used as abroad- spectrum antibiotic possessing activityagainst many Gram- negative and Gram- positivemicroorganisms. (± ) - 2 - Acetamido- 3 - hydroxy- 1 -(4- nitrophenyl) - 1 - propanone[(± ) - 1 ]is one of theintermediates of producing chloramphenicol.Petrow et al.[2 ] reported some transformations of(± ) - 1 in hydrolysis reactions. However,thereaction products were complicated under multiplehydr…     

激光诱导荧光法研究CN(V″=0,1)自由基与碳氢化合物的反应速率和机理

The rate constants of eleven hydrocarbons and fluorocarbons with CN (V″=0, 1) at 300 K have been measured by using Laser Induced Fluorescence(LIF) method For the saturated hydrocarbons, the rate constants are changed from (5.6±0.3)×10~(-13) for CH_4 to (2.3±0.2)×10~(-10)cm~3 molecu~(-1).s~(-1) for C_7H_(16). The rate constants of the reaction of CN with alkenes and alkynes are close to the gas kinetic rate in spite of the structure of the molecules.The rate constants and mechanism of CN with the saturated hydrocarbons, H_2 and CH_3OH can be explained satisfactorily by the long distance attractive potential. The reaction of CN with alkenes and alkynes can only proceed through the addition into π bond. The influence of vibrational energy on the reaction rate was not found in the reactions of CN radical with hydrocarbon compounds.     

Experimental evidence for the pressure dependence of the reaction rate constant between acetic acid and hydroxyl radicals

The reaction rate constant of acetic acid with the hydroxyl radical is measured at 93 Torr with our high-pressure flow system (HPFS) and found to display a negative temperature dependence that can be described by the Arrhenius expression, k(T) = (2.44 ± 0.22) × 10(-14) exp ((1027 ± 24)/T)) cm(3) molecule(-1) s(-1). Compared with our previously reported 7 Torr data, we find a noticeable pressure dependence. This dependence is observed to increase with decreasing temperature. This finding is consistent with a termolecular reaction mechanism. It is the first experimental evidence of the pressure dependence for this rate constant. A kinetics model is constructed, and the model results agree qualitatively with our experimental data. The extrapolated rate constant of the title reaction would be faster than previously believed at conditions of the upper troposphere/lower stratosphere, suggesting that the importance of acetic acid in its impact on HO(x) chemistry is currently underestimated.     

Identification of binding sites for acetaldehyde adsorption on titania nanorod surfaces using CIMS

The interaction of acetaldehyde with TiO(2) nanorods has been studied under low pressures (acetaldehyde partial pressure range 10(-4)-10(-8) Torr) using chemical ionization mass spectrometry (CIMS). We quantitatively separate irreversible adsorption, reversible adsorption, and an uptake of acetaldehyde assigned to a thermally activated surface reaction. We find that, at room temperature and 1.2 Torr total pressure, 2.1 ± 0.4 molecules/nm(2) adsorb irreversibly, but this value exhibits a sharp decrease as the analyte partial pressure is lowered below 4 × 10(-4) Torr, regardless of exposure time. The number of reversible binding sites at saturation amounts to 0.09 ± 0.02 molecules/nm(2) with a free energy of adsorption of 43.8 ± 0.2 kJ/mol. We complement our measurements with FTIR spectroscopy and identify the thermal dark reaction as a combination of an aldol condensation and an oxidative adsorption that converts acetaldehyde to acetate or formate and CO, at a measured combined initial rate of 7 ± 1 × 10(-4) molecules/nm(2) s. By characterizing binding to different types of sites under dark conditions in the absence of oxygen and gas phase water, we set the stage to analyze site-specific photoefficiencies involved in the light-assisted mineralization of acetaldehyde to CO(2).     

Gas-phase photodissociation of CH3COCN at 308 nm by time-resolved Fourier-transform infrared emission spectroscopy

By using time-resolved Fourier-transform infrared emission spectroscopy, the fragments of HCN(v = 1, 2) and CO(v = 1-3) are detected in one-photon dissociation of acetyl cyanide (CH(3)COCN) at 308 nm. The S(1)(A(")), (1)(n(O), π(?) (CO)) state at 308 nm has a radiative lifetime of 0.46 ± 0.01 μs, long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of Ar collision-induced internal conversion is estimated to be (1-7) × 10(-12) cm(3) molecule(-1) s(-1). The measurements of O(2) dependence exclude the production possibility of these fragments via intersystem crossing. The high-resolution spectra of HCN and CO are analyzed to determine the ro-vibrational energy deposition of 81 ± 7 and 32 ± 3 kJ∕mol, respectively. With the aid of ab initio calculations, a two-body dissociation on the energetic ground state is favored leading to HCN + CH(2)CO, in which the CH(2)CO moiety may further undergo secondary dissociation to release CO. The production of CO(2) in the reaction with O(2) confirms existence of CH(2) and a secondary reaction product of CO. The HNC fragment is identified but cannot be assigned, as restricted to a poor signal-to-noise ratio. Because of insufficient excitation energy at 308 nm, the CN and CH(3) fragments that dominate the dissociation products at 193 nm are not detected.     

The lowest-lying electronic singlet and triplet potential energy surfaces for the HNO-NOH system: energetics, unimolecular rate constants, tunneling and kinetic isotope effects for the isomerization and dissociation reactions

The lowest-lying electronic singlet and triplet potential energy surfaces (PES) for the HNO-NOH system have been investigated employing high level ab initio quantum chemical methods. The reaction energies and barriers have been predicted for two isomerization and four dissociation reactions. Total energies are extrapolated to the complete basis set limit applying focal point analyses. Anharmonic zero-point vibrational energies, diagonal Born-Oppenheimer corrections, relativistic effects, and core correlation corrections are also taken into account. On the singlet PES, the (1)HNO → (1)NOH endothermicity including all corrections is predicted to be 42.23 ± 0.2 kcal mol(-1). For the barrierless decomposition of (1)HNO to H + NO, the dissociation energy is estimated to be 47.48 ± 0.2 kcal mol(-1). For (1)NOH → H + NO, the reaction endothermicity and barrier are 5.25 ± 0.2 and 7.88 ± 0.2 kcal mol(-1). On the triplet PES the reaction energy and barrier including all corrections are predicted to be 7.73 ± 0.2 and 39.31 ± 0.2 kcal mol(-1) for the isomerization reaction (3)HNO → (3)NOH. For the triplet dissociation reaction (to H + NO) the corresponding results are 29.03 ± 0.2 and 32.41 ± 0.2 kcal mol(-1). Analogous results are 21.30 ± 0.2 and 33.67 ± 0.2 kcal mol(-1) for the dissociation reaction of (3)NOH (to H + NO). Unimolecular rate constants for the isomerization and dissociation reactions were obtained utilizing kinetic modeling methods. The tunneling and kinetic isotope effects are also investigated for these reactions. The adiabatic singlet-triplet energy splittings are predicted to be 18.45 ± 0.2 and 16.05 ± 0.2 kcal mol(-1) for HNO and NOH, respectively. Kinetic analyses based on solution of simultaneous first-order ordinary-differential rate equations demonstrate that the singlet NOH molecule will be difficult to prepare at room temperature, while the triplet NOH molecule is viable with respect to isomerization and dissociation reactions up to 400 K. Hence, our theoretical findings clearly explain why (1)NOH has not yet been observed experimentally.     

Atmospheric chemistry of two biodiesel model compounds: methyl propionate and ethyl acetate

The atmospheric chemistry of two C(4)H(8)O(2) isomers (methyl propionate and ethyl acetate) was investigated. With relative rate techniques in 980 mbar of air at 293 K the following rate constants were determined: k(C(2)H(5)C(O)OCH(3) + Cl) = (1.57 ± 0.23) × 10(-11), k(C(2)H(5)C(O)OCH(3) + OH) = (9.25 ± 1.27) × 10(-13), k(CH(3)C(O)OC(2)H(5) + Cl) = (1.76 ± 0.22) × 10(-11), and k(CH(3)C(O)OC(2)H(5) + OH) = (1.54 ± 0.22) × 10(-12) cm(3) molecule(-1) s(-1). The chlorine atom initiated oxidation of methyl propionate in 930 mbar of N(2)/O(2) diluent (with, and without, NO(x)) gave methyl pyruvate, propionic acid, acetaldehyde, formic acid, and formaldehyde as products. In experiments conducted in N(2) diluent the formation of CH(3)CHClC(O)OCH(3) and CH(3)CCl(2)C(O)OCH(3) was observed. From the observed product yields we conclude that the branching ratios for reaction of chlorine atoms with the CH(3)-, -CH(2)-, and -OCH(3) groups are <49 ± 9%, 42 ± 7%, and >9 ± 2%, respectively. The chlorine atom initiated oxidation of ethyl acetate in N(2)/O(2) diluent gave acetic acid, acetic acid anhydride, acetic formic anhydride, formaldehyde, and, in the presence of NO(x), PAN. From the yield of these products we conclude that at least 41 ± 6% of the reaction of chlorine atoms with ethyl acetate occurs at the -CH(2)- group. The rate constants and branching ratios for reactions of OH radicals with methyl propionate and ethyl acetate were investigated theoretically using transition state theory. The stationary points along the oxidation pathways were optimized at the CCSD(T)/cc-pVTZ//BHandHLYP/aug-cc-pVTZ level of theory. The reaction of OH radicals with ethyl acetate was computed to occur essentially exclusively (～99%) at the -CH(2)- group. In contrast, both methyl groups and the -CH(2)- group contribute appreciably in the reaction of OH with methyl propionate. Decomposition via the α-ester rearrangement (to give C(2)H(5)C(O)OH and a HCO radical) and reaction with O(2) (to give CH(3)CH(2)C(O)OC(O)H) are competing atmospheric fates of the alkoxy radical CH(3)CH(2)C(O)OCH(2)O. Chemical activation of CH(3)CH(2)C(O)OCH(2)O radicals formed in the reaction of the corresponding peroxy radical with NO favors the α-ester rearrangement.     

Lu(Et2dtc)3(phen)的生成反应焓变、摩尔热容和恒容燃烧能测定

A ternary solid complex Lu(Et₂dtc)₃(phen) has been obtained from the reaction of hydrated lutetium chloride with sodium diethyldithiocarbamate (NaEt₂dtc), and 1,10-phenanthroline (o-phen·H₂O) in absolute ethanol. IR spectrum of the complex indicates that Lu³⁺ binds with sulfur atom in the Na(Et₂dtc)₃ and nitrogen atom in the o-phen. The enthalpy change of liquid-phase reaction of formation of the complex, Δ_rH_m^Ө (l), was determined to be (-32.821 ± 0.147 ) kJ·mol^-1 at 298.15 K by an RD-496 Ⅲ type heat conduction microcalormeter. The enthalpy change of the solid-phase reaction of formation of the complex, Δ_rH_m^Ө (s), was calculated to be (104.160 ± 0.168) kJ · mol^-1 on the basis of an appropriate thermochemistry cycle. The thermodynamics of liquid-phase reaction of formation of the complex was investigated by changing the temperature of liquid-phase reaction. Fundamental parameters, such as the activation enthalpy (ΔH_≠^Ө), the activation entropy (ΔS_≠^Ө), the activation free energy (ΔG_≠^Ө), the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A) and the reaction order (n), were obtained by combination the reaction thermodynamic and kinetic equations with the data of thermokinetic experiments. The molar heat capacity of the complex, c_m, was determined to be (82.23 ± 1.47) J·mol^-1·K^-1 by the same microcalormeter. The constant-volume combustion energy of the complex, Δ_cU, was determined as (-17 898.228 ± 8.59) kJ·mol^-1 by an RBC-Ⅱtype rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_cH_m^Ө, and standard enthalpy of formation, Δ_fH_m^Ө, were calculated to be (-17 917.43 ± 8.11) kJ·mol^-1 and (-859.95 ±10.12) kJ·mol^-1, respectively.     

Abstraction kinetics of H-atom by OH radical from pinonaldehyde (C10H16O2): ab initio and transition-state theory calculations

The kinetics and abstraction rate coefficients of hydroxyl radical (OH) reaction with pinonaldehyde were computed using G3(MP2) theory and transition-state theory (TST) between 200 and 400 K. Structures of the reactants, reaction complexes (RCs), product complexes (PCs), transition states (TSs), and products were optimized at the MP2(FULL)/6-31G* level of theory. Fifteen transition states were identified for the title reaction and confirmed by intrinsic reaction coordinate (IRC) calculations. The contributions of all the individual hydrogens in the substrate molecule to the total reaction are computed. The quantum mechanical tunneling effect was computed using Wigner's and Eckart's methods (both symmetrical and unsymmetrical methods). The reaction exhibits a negative temperature dependent rate coefficient, k(T) = (1.97 ± 0.34) × 10(-13) exp[(1587 ± 48)/T] cm(3) molecule(-1) s(-1), k(T) = (3.02 ± 0.56) × 10(-13) exp[(1534 ± 52/T] cm(3) molecule(-1) s(-1), and k(T) = (4.71 ± 1.85) × 10(-14) exp[(2042 ± 110)/T] cm(3) molecule(-1) s(-1) with Wigner's, Eckart's symmetrical, and Eckart's unsymmetrical tunneling corrections, respectively. Theoretically calculated rate coefficients are found to be in good agreement with the experimentally measured ones and other theoretical results. It is shown that hydrogen abstraction from -CHO position is the major channel, whereas H-abstraction from -COCH(3) is negligible. The atmospheric lifetime of pinonaldehyde is computed to be few hours and found to be in excellent agreement with the experimentally estimated ones.     

Integration of catalysis and analysis is the key: rapid and precise investigation of the catalytic asymmetric Gosteli-Claisen rearrangement

The kinetics of the Cu(II)(bisoxazoline)-catalyzed diastereo- and enantioselective Gosteli-Claisen rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ethers has been investigated by enantioselective on-column reaction gas chromatography (ocRGC). Enantioselective ocRGC integrates (stereoselective) catalysis and enantioselective chromatography in a single microcapillary, which is installed in a GC-MS for direct analysis of conversion and selectivity. Thus, this technique allows direct differentiation of thermal and stereoselectively catalyzed reaction pathways and determination of activation parameters and selectivities of the individual reaction pathways starting from stereoisomeric reactants with high precision. Two modes of operation of enantioselective ocRGC are presented to investigate noncatalyzed, i.e., conversion of isopropyl-2-(allyloxy)but-2Z-enoate 1 to isopropyl-3R,S-methyl-2-oxy-hex-5-enoate (±)-2 and the [Cu{(R,R)-Ph-box}](SbF(6))(2)-catalyzed Gosteli-Claisen rearrangement, i.e., conversion of isopropyl-2-(but-2'E-en-1-yloxy)but-2Z-enoate (E,Z)-3 to isopropyl-3S,4S-dimethyl-2-oxy-hex-5-enoate 4b. Eyring activation parameters have been determined by temperature-dependent measurements: Uncatalyzed rearrangement of 1 to (±)-2 gives ΔG(?) (298 K) = 114.1 ± 0.2 kJ·mol(-1), ΔH(?) = 101.1 ± 1.9 kJ·mol(-1), and ΔS(?) = -44 ± 5 J·(K·mol)(-1), and catalyzed rearrangement of (E,Z)-3 to 4b gives ΔG(?)(298 K) = 101.1 ± 0.3 kJ·mol(-1), ΔH(?) = 106.1 ± 6.6 kJ·mol(-1), and ΔS(?) = 17 ± 19 J·(K·mol)(-1).     

Highly stereocontrolled and regiocontrolled syntheses of 2,3,4-trisubstituted alkanoates and lactones

New chlorodiols (±)-3 and (±)-5 are densely functionalized and versatile synthons. They are converted in one step on a gram scale into 2-chlorolactones (±)-6 and (±)-7 and into 4-hydroxy glycidate esters (±)-9 and (±)-10. The 4-hydroxy glycidate esters (±)-9 and (±)-10 are converted stereospecifically and regiospecifically into oxazolines (±)-13 and (±)-14 and into cyclic carbamates (±)-18-(±)-20. The 4-hydroxy glycidate ester (±)-10 undergoes stereocontrolled and regiocontrolled epoxide opening by sodium azide to form the 2-azido-3,4-dihydroxy alkanoate (±)-21. Finally, chlorodiol (±)-5 reacts stereospecifically with silver triflate to form the 2,3-dihydroxyfuranone (±)-26.