The kinetics of the addition of alkyl radicals to carbonyl groups. Part I. The addition of methyl radicals to hexafluoroacetone in the gas phase. The formation of the hexafluoro-t-butoxy radical

By pyrolyzing di-t-butyl peroxide over the temperature range of 405–450 K in the presence of hexafluoroacetone the kinetics of the addition reaction (1), CH₃ + (CF₃)₂CO→; (CF₃)₂C(?)CH₃, have been studied. Detailed analyses have shown that the principal product of the adduct radical, (CF₃)₂C(?)CH₃, is CF₃COCH₃ from reaction (2), (CF₃)₂C(?)CH₃ → CF₃COCH₃ + CF₃. The rate constant of the addition reaction was determined to be k₁(dm³/mol·s) = (1.1 ± 4.0) + 10⁹ exp(-(3680 ± 480)/T) over the temperature range 405–450 K, based on the value k₃ = 2.2 × 10¹⁰ dm³/mol·s for reaction (3), 2CH₃ → C₂H₆. The results are discussed in relation to existing data for radical additions to carbonyl groups.     

The kinetics of the addition of alkyl radicals to carbonyl groups. II. The addition of methyl radicals to trifluoroacetone in the gas phase. The formation reaction of the trifluoro-t-butoxy radical

By photolyzing azomethane over the temperature range 331–491 K in the presence of trifluoroacetone the kinetics of the addition reaction (1), ?H₃ + CF₃COCH₃ → CF₃C(?)(CH₃)₂ have been studied. Detailed analyses have shown that the principal product of the adduct radical, CF₃C(?)(CH₃)₂, is CH₃COCH₃ from reaction (?2), CF₃C(?)(CH₃)₂ → CH₃COCH₃ + ?F₃. The rate constant of the addition reaction has been determined to be k₁(dm³/mol s) = (4.5 ± 1.4) × 10⁷ exp(-(3370 ± 120)/T) over the temperature range 331–491 K, based on the value k₃ = 2.2 × 10¹⁰ dm³/mol s for the reaction (3), 2?H₃ → C₂H₆. The results are discussed in relation to existing data for radical additions to groups.     

The gas-phase decomposition of methylsilane. Part III. Kinetics

The homogeneous gas-phase decomposition kinetics of methylsilane and methylsilane-d₃ have been investigated by the comparative-rate-single-pulse shock-tube technique at total pressures of 4700 torr in the 1125–1250 K temperature range. Three primary processes occur: CH₃SiH₃ → CH₃SiH + H₂ (1), CH₃SiH₃ → CH₄ + SiH₂ (2), and CH₃SiH₃ → CH₂ = SiH₂ + H₂ (3). The high-pressure rate constants for the primary processes in CH₃SiH₃ obtained by RRKM calculations are log (k₁ + k₃) (s^?1) = 15.2 - 64,780 Cal/θ and log k₂ (s^?) = 14.50 - 67,600 → 2800 Cal/θ. For CH₃SiD₃ these same rate constants are log k₁ (s^?) = 14.99 - 64,700 cal/θ log k₂ (s^?) = 14.68 – 66,700 → 2000 cal/θ, and log k₃ (s^?) = 14.3 ? 64,700 cal/θ.     

Dynamics of the CH3 + OH reaction

We study dynamics of the CH₃ + OH reaction over the temperature range of 300–2500 K using a quasiclassical method for the potential energy composed of explicit forms of short‐range and long‐range interactions. The explicit potential energy used in the study gives minimum energy paths on potential energy surfaces showing barrier heights, channel energies, and van der Waals well, which are consistent with ab initio calculations. Approximately, 20% of CH₃ + OH collisions undergo OH dissociation in a direct‐mode mechanism on a subpicosecond scale (<50 fs) with the rate coefficient as high as ～10^?10 cm³ molecule^?1 s^?1. Less than 10% leads to the formation of excited intermediates CH₃OH? with excess vibrational energies in CO and OH bonds. CH₃OH? stabilizes to CH₃OH, redissociates back to reactants, or forms one of various products after intramolecular energy redistribution via bond dissociation and formation on the time scale of 50–200 fs. The principal product is ¹CH₂ (k being ～10^?11), whereas ks for CH₂OH, CH₂O, and CH₃O are ～10^?12. The minor products are HCOH and CH₄ (k～10^?13). The total rate coefficient for CH₃ + OH → CH₃OH? → products is ～10^?11 and is weakly dependent on temperature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 455–466, 2011     

Gas‐phase reactions of Cl atoms with propane,n‐butane,and isobutane

Using the relative kinetic method, rate coefficients have been determined for the gas‐phase reactions of chlorine atoms with propane, n‐butane, and isobutane at total pressure of 100 Torr and the temperature range of 295–469 K. The Cl₂ photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm³ molecule^?1 s^?1) have been derived: (7.4 ± 0.2) × 10^?11 exp [‐(70 ± 11)/ T], Cl + C₃H₈ → HCl + CH₃CH₂CH₂; (5.1 ± 0.5) × 10^?11 exp [(104 ± 32)/ T], Cl + C₃H₈ → HCl + CH₃CHCH₃; (7.3 ± 0.2) × 10^?11 exp[?(68 ± 10)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃ CH₂CH₂CH₂; (9.9 ± 2.2) × 10^?11 exp[(106 ± 75)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃CH₂CHCH₃; (13.0 ± 1.8) × 10^?11 exp[?(104 ± 50)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CHCH₃CH₂; (2.9 ± 0.5) × 10^?11 exp[(155 ± 58)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CCH₃CH₃ (all error bars are ± 2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 651–658, 2002     

High temperature pyrolysis of methane in shock waves. Rates for dissociative recombination reactions of methyl radicals and for propyne formation reaction

The pyrolysis of 2% CH₄ and 5% CH₄ diluted with Ar was studied using both a single–pulse and time–resolved spectroscopic methods over the temperature range 1400–2200 K and pressure range 2.3–3.7 atm. The rate constant expressions for dissociative recombination reactions of methyl radicals, CH₃ + CH₃ → C₂H₅ + H and CH₃ + CH₃ → C₂H₄ + H₂, and for C₃H₄ formation reaction were investigated. The simulation results required considerably lower value than that reported for CH₃ + CH₃ → C₂H₄ + H₂. Propyne formation was interpreted well by reaction C₂H₂ + CH₃ → P-C₃H₄ + H with ?? = 6.2 × ¹⁰12 exp(?17 kcal/RT) ^cm3 mol^?1 s^?1.     

The gas-phase pyrolysis of alkyl nitrites. IV. Ethyl nitrite

The rate of decomposition of methyl nitrite (MN) has been studied in the presence of isobutane-t-BuH-(167-200°C) and NO (170-200°C). In the presence of t-BuH (～0.9 atm), for low concentrations of MN (～10^?4M) and small extents of reaction (4-10%), the first-order homogeneous rates of methanol (MeOH) formation are a direct measure of reaction (1) since k₄(t-BuH) »k₂(NO): . The results indicate that the termination process involves only \documentclass{article}\pagestyle{empty}\begin{document}$ t - {\rm Bu\, and\, NO:\,\,}t - {\rm Bu} + {\rm NO\stackrel{e}{\longrightarrow}} $\end{document} products, such that k_e ～ 10¹⁰ M^?1 ～ sec^?1.Under these conditions small amounts of CH₂O are formed (3-8% of the MeOH). This is attributed to a molecular elimination of HNO from MN. The rate of MeOH formation shows a marked pressure dependence at low pressures of t-BuH. Addition of large amounts of NO completely suppresses MeOH formation. The rate constant for reaction (1) is given by k₁ = 10^{15.8°0.6-41.2°1}/· sec^?1. Since (E₁ + RT) and ΔH^Δ₁ are identical, within experimental error, both may be equated with D(MeO - NO) = 41.8 + 1 kcal/mole and E₂ = 0 ± 1 kcal/mol. From ΔS¹₁ and A₁, k₂ is calculated to be 10^10.1°0.6M^?1 · sec^?1, in good agreement with our values for other alkyl nitrites. These results reestablish NO as a good radical trap for the study of the reactions of alkoxyl radicals in particular. From an independent observation that k₆/k₂ = 0.17 independent of temperature, we conclude that \documentclass{article}\pagestyle{empty}\begin{document}$ E_6 = 0 \pm 1{\rm kcal}/{\rm mol\, and\,}\,k_6 = 10^{9.3} M^{- 1} \cdot {\rm sec}^{- 1} :{\rm MeO} + {\rm NO}\stackrel{6}{\longrightarrow}{\rm CH}_2 {\rm O} + {\rm HNO} $\end{document}. From the independent observations that k₂:k_2→: k_6→ was 1:0.37:0.04, we find that k_2→ = 10^9.7M^?1 ? sec^?1 and k_6→ = 10^8.7M^?1 ? sec^?1. In addition, the thermodynamics lead to the result In the presence of NO (～0.9 atm) the products are CH₂O and N₂O (and presumably H₂O) such that the ratio N₂O/CH₂O ～ 0.5. The rate of CH₂O formation was affected by the surface-to-volume ratio s/v for different reaction vessels, but it is concluded that, in a spherical reaction vessel, the CH₂O arises as the result of an essentially homogeneous first-order, fourcenter elimination of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm HNO}:{\rm MN\stackrel{5}{\longrightarrow}CH}_{\rm 2} {\rm O} + {\rm HNO} $\end{document}. The rate of CH₂O formation is given by k₅ = 10^{13.6°0.6-38.5-1}/? sec^?1.     

The reaction of methoxy radicals with nitric oxide and nitrogen dioxide

By allowing dimethyl peroxide (10^?4M) to decompose in the presence of nitric oxide (4.5 × 10^?5M), nitrogen dioxide (6.5 × 10^?5M) and carbon tetrafluoride (500 Torr), it has been shown that the ratio k₂/k_2′ = 2.03 ± 0.47: CH₃O + NO → CH₃ONO (reaction 2) and CH₃O + NO₂ → CH₃ONO₂ (reaction 2′). Deviations from this value in this and previous work is ascribed to the pressure dependence of both these reactions and heterogeneity in reaction (2). In contrast no heterogeneous effects were found for reaction (2′) making it an ideal reference reaction for studying other reactions of the methoxy radical. We conclude that the ratio k₂/k_2′ is independent of temperature and from k₁ = 10^10.2±0.4M^?1 sec^?1 we calculate that k_2′ = 10^9.9±0.4M^?1 sec^?1. Both k₂ and k_2′ are pressure dependent but have reached their limiting high-pressure values in the presence of 500 Torr of carbon tetrafluoride. Preliminary results show that k₄ = 10.^9.0±0.6 10^?4.5±1.1/ΘM^?1 sec^?1 (Θ = 2.303RT kcal mole^?1) and by k₄ = 10^8.6±0.6 10^?2.4±1.1/ΘM^?1 sec^?1: CH₃O + O₂ → CH₂O + HO₂ (reaction 4) and CH₃O + t-BuH → CH₃OH + (t-Bu) (reaction 4′).     

The effect of temperature on formaldehyde photooxidation in oxygen-lean atmospheres

The photooxidation of formaldehyde in CH₂O? O₂, oxygen-lean mixtures was studied in the temperature range 298–378 K. H₂ and CO formation and the loss of O₂ proceed by a chain mechanism, which between 328 and 378 K follows the previously suggested kinetics [1] with one modification. The reaction HO₂ + CH₂O ? HO₂CH₂O (5) is now assumed to be reversible and ΔH is estimated to be between 14 and 19 kcal/mol. The relative yields of the chain formed H₂ and CO and of the consumed O₂ remained constant over the entire temperature range indicating that the relative efficiencies of the HO reactions: HO + CH₂O → H₂O HCO? (7), HO + CH₂O → H₂O + HCO (8) and HO + CH₂O → HOCH₂O (9) are temperature independent.     

Photoexcitation and photodissociation lasers. III. mechanisms of CO laser emission from the vacuum UV photodissociation of CH2COO2 and CH2COSO2 mixtures

CO laser emission was detected in the vacuum UV flash photolysis of CH₂CO. The emission is attributed to the initial photodissociation reaction

Addition of O₂ to the CH₂CO system caused a pronounced enhancement in the laser intensity. This effect is believed to be due to the removal of the CH₂ + CH₂CO reaction, which produces uninverted CO molecules. A greater laser output was obtained when SO₂ was used instead of O₂. In the O₂-added system, a total of 16 transitions ranging from Δv(8→7) to (4→3) were identified. Addition of SO₂ increased the total number of lines to 34, lasing in the range between (11→10) and (4→3). This enhancement is ascribed to the occurrence of the reaction

In addition to these chemical effects, the effects of flash energy, inert gases and total pressures have been investigated.     

Unusual H2-forming chain reaction in the 3130-Å photolysis of formaldehyde-oxygen mixtures at 25°C

A kinetic study has been made of the 3130-Å photolysis of CH₂O (8 torr) in O₂-containing mixtures (0.02–8 torr) and in the presence of added CO₂ (0–300 torr) at 25°C. Quantum yields of formation of H₂, CO, and CO₂ and the loss of O₂ were measured. Φ and Φ_CO were much above unity. In an explanation of these unexpected results, a new H-atom-forming chain mechanism was postulated involving HO₂ and HO addition to CH₂O: CH₂O + hν → H + HCO (1) H + CH₂O → H₂ + HCO (3) H + O₂ + M → HO₂ + M (6) HCO + O₂ → HO₂ + CO (8) HO₂ + CH₂O → (HO₂CH₂O) → HO + HCO₂H (15) HO + CH₂O → H₂O + HCO? (16); HCO? → H + CO (19) HO + CH₂O → H₂O + HCO (17) and HO + CH₂O → HCO₂H + H (18). When the results are rationalized in terms of this mechanism, the data suggest k₁₆ ? k₁₇ and k₁₆/k₁₈ ? 0.5. The data require that a reassessment of the relative rates of reactions (7) and (8) be made, since in the previous work HCO₂H formation was used as a monitor of the rate of reaction (7) HCO + O₂ + M → HCOO₂ + M (7). The present data from experiments at P = 8 torr and P = 1–4 torr give k₇[M]/(k₇[M] + k₈) ≥ 0.049 ± 0.017. These data coupled with the k₈ estimates of Washida and coworkers give k₇ ≥ (4.4 ± 1.6) × 10¹¹ l²/mol²·sec for M = CH₂O. The reaction sequence proposed here is consistent with the observed deterimental effect of O₂ addition on the laser-induced isotope enrichment in HDCO. In additional studies of CH₂O-O₂-isobutene mixtures it was found that Φ was equal to ?₂ as estimated in O₂-free CH₂O-isobutene mixtures. These results suggest that the increase in CO (ν = 1) product observed with O₂ addition in CH₂O photolysis does not result from perturbations in the fragmentation pattern of the excited CH₂O, but it is likely that it originates in the occurrence of the exothermic reaction HCO + O₂ → HO₂ + CO (ν = 1).     

High‐Temperature Rate Constants for H + Tetramethylsilane and H + Silane and Implications about Structure–Activity Relationships for Silanes

The shock‐tube technique has been used to investigate the reactions H + SiH₄ → H₂ + SiH₃ (R1) and H + Si(CH₃)₄ → Si(CH₃)₃CH₂ + H₂ (R2) behind reflected shock waves. C₂H₅I was used as a thermal in situ source for H atoms. For reaction (R1), the experiments covered a temperature range of 1170–1251 K and for (R2) 1227–1320 K. In both cases, the pressures were near 1.5 bar. In these experiments, H atoms were monitored with atomic resonance absorption spectrometry. Fits to the H‐atom temporal concentration profiles applying postulated chemical kinetic reaction mechanisms were used for determining the rate constants k₁ and k₂. Experimental rate constants were well represented by the Arrhenius equations k₁(T) = 2.75 × 10⁻⁹ exp(−37.78 kJ mol⁻¹/RT) cm³ s⁻¹ and k₂(T) = 1.17 × 10⁻⁷ exp(−86.82 kJ mol⁻¹/RT) cm³ s⁻¹. Transition state theory (TST) calculations based on CBS‐QB3 and G4 levels of theory show good agreement with experimentally obtained rate constants; the experimental values for k₁ and k₂ are ∼40% lower and ∼50% larger than theoretical predictions, respectively. For the development of a mechanism describing the thermal decomposition of tetramethylsilane (Si(CH₃)₄; TMS), also TST‐based rate constants for reaction CH₃ + Si(CH₃)₄ → Si(CH₃)₃CH₂ + CH₄ (R3) were calculated. A comparison between experimental and theoretical rate constants k₂ and k₃ with available rate constants from the literature indicates that Si(CH₃)₄ has very similar reactivity toward H abstractions like neopentane (C(CH₃)₄), which is the analog hydrocarbon to TMS. Based on these results, the possibility of drawing reactivity analogies between hydrocarbons and structurally similar silicon‐organic compounds for H‐atom abstractions is discussed.     

Kinetic study of the reaction of IO with CH3SCH3

The reaction IO + CH₃SCH₃ → products (3) was studied at room temperature and near 1 Torr pressure of He, using the discharge flow mass spectrometric technique. The rate constant was found to be k₃ = (1.5 ± 0.5) × 10^?11 cm³ molecule^?1 s^?1. CH₃S(O)CH₃ was detected as a product suggesting the following channel: IO + CH₃SCH₃ → CH₃S(O)CH₃ + I. The rate constant of the reaction IO + IO → products (1) was also measured: k₁ = (3 ± 0.5) × 10^?11 at 298 K and 1 Torr pressure. The atmospheric implication of reaction (3) is discussed. The results indicate that this reaction could be a potential important sink of CH₃SCH₃ in marine atmosphere.     

Reaction of excited iodine atoms with methyl iodide: Rate constant determinations

The rate constant for the reaction I(²P_1/2) + CH₃I → I₂ + CH₃ has been reevaluated taking into account both collisional deactivation of excited iodine atoms and loss of I₂ by I₂ + CH₃ → I + CH₃I. The reevaluation is based upon data obtained (R. T. Meyer), J. Chem. Phys., 46 , 4146 (1967) from the flash photolysis of CH₃I using time-resolved mass spectrometry to measure the rate of I₂ formation. Computer simulations of the complete kinetic system and a closed-form solution of a simplified set of the differential equations yielded a value of 6(± 4) × 10⁶ 1./mole-sec for the excited iodine atom reaction in the temperature region of 316 to 447 K. A slight temperature dependence was observed, but an activation energy could not be evaluated quantitatively due to the small temperature range studied. An upper limit for the collisional deactivation of I(²P_1/2) with CH₃I was also determined (2.4 × 10⁷ 1./mole-sec).     

Glycosylidene Carbenes. Part 6. Synthesis of alkyl and fluoroalkyl glycosides

The syntheses of glycosides from the diazirine 1 and a range of alcohols under thermal and/or photolytic conditions are described. Yields and diastereoselectivities depend upon the pK_HA values of the alcohols, the solvent, and the reaction temperature. The glycosidation of weakly acidic alcohols (MeOH, EtOH, i-PrOH, and t-BuOH, 1 equiv. each) in CH₂Cl₂ at room temperature leads to the glycosides 2–5 in yields between 60 and 34% (Scheme 1 and Table 1). At ?70 to ?60°, yields are markedly higher. In CH₂Cl₂, diastereoselectivities are very low. In THF, at ?70 to ?60°, however, glycosidation of i-PrOH leads to α-D -/β-D - 4 in a ratio of 8:92. More strongly acidic alcohols, such as CF₃CH₂OH, (CF₃)₂ CHOH, and (CF₃)₂C(Me)OH, and the highly fluorinated long-chain alcohols CF₃(CF₂)₅(CH₂)₂OH ( 11 ) and CHF₂(CF₂)₉CH₂OH ( 13 ) react (CH₂Cl₂, r.t.) in yields between 73 and 85% and lead mainly to the β-D -glucosides β-D - 6 to β-D - 8 , β-D - 12 , and β-D - 14 (d.e. 14–68%). Yields and diastereoselectivities are markedly improved, when toluene, dioxane, 1,2-dimetoxyethane, or THF are used, as examined for the glycosidation of (CF₃)₂C(Me)OH, yielding (1,2-dimethoxyethane, 25°) 80% of α-D -/ β-D - 8 in a ratio of 2:98 (d.e. 96%; Table 4). In EtCN, (CF₃)₂C(Me)OH yields up to 55% of the imidate 10 . Glycosidation of di-O-isopropylideneglucose 15 leads to 16 (CH₂Cl₂, r.t.; 65%, α-D / β-D = 33:67). That glycosidation occurs by initial protonation of the intermediate glycosylidene carbene is evidenced, for strongly acidic alcohols, by the formation of 10 , derived from the attack of (CF₃)₂MeCO^? on an intermediate nitrilium ion (Scheme 4), and for weakly acidic alcohols, by the formation of α-D - 9 and β-D - 9 , derived by attack of i-PrO^? on intermediate tetrahydrofuranylium ions. A working hypothesis is presented (Scheme 3). The diastereoselectivities are rationalized on the basis of a protonation in the σ plane of the intermediate carbene, the stabilization of the thereby generated ion pair by interaction with the BnO? C(2) group, with the solvent, and/or with the alcohol, and the final nucleophilic attack by RO^? in the π plane of the (solvated) oxonium ion.     

Glycosylidene Carbenes. Part 23. Regioselective glycosidation of deoxy- and fluorodeoxy-myo-inositol derivatives

To demonstrate the relevance of the kinetic acidity of individual OH groups for the regioselectivity of glycosylation by glycosylidene carbenes, we compared the glycosylation by 1 of the known triol 2 with the glycosylation of the diol D - 3 and the fluorodiol L - 4 . Deoxygenation with Bu₃SnH of the phenoxythiocarbonyl derivative of 5 (Scheme 1) or the carbonothioate 6 gave the racemic alcohol (±)- 7 . The enantiomers were separated via the allophanates 9a and 9b , and desilylated to the deoxydiols D - and L - 3 , respectively. The assignment of their absolute configuration is based upon the CD spectra of the bis(4-bromobenzoates) D - and L - 10 . The (+)-(R)-1-phenylethylcarbamates 13a and 13b (Scheme 2) were prepared from the fluoroinositol (±)- 11 via (±)- 4 and the silyl ether (±)- 12 and separated by chromatography. The absolute configuration of 13a was established by X-ray analysis. Decarbamoylation of 13a ( → L - 12 ) and desilylation afforded the fluorodiol L - 4 . The H-bonds of D - 3 and L - 4 in chlorinated solvents and in dioxane were studied by IR and ¹H-NMR spectroscopy (Fig. 2). In both diols, HO? C(2) forms an intramolecular, bifurcated H-bond. There is an intramolecular H-bond between HO? C(6) and F in solutions of L - 4 in CH₂Cl₂, but not in 1,4-dioxane; the solubility of L - 4 in CH₂Cl₂ is too low to permit a meaningful glycosidation in this solvent. Glycosidation of D - 3 in dioxane by the carbene derived from 1 (Scheme 3) followed by acetylation gave predominantly the pseudodisaccharides 18/19 (38%), derived from glycosidation of the axial OH group besides the pseudodisaccharides 16 / 17 (13%) and the epoxides 20 / 21 (7%), derived from protonation of the carbene by the equatorial OH group. Similarly, the reaction of L - 4 with 1 (Scheme 4) led to the pseudodisaccharides 28 / 29 (46%) and 26 / 27 (14%), derived from deprotonation of the axial and equatorial OH groups, respectively. Formation of the epoxides involved deprotonation of the intramolecularly H-bonded tautomer, followed by intramolecular alkylation, elimination, and substitution (Scheme 4). The regio- and diastereoselectivities of the glycosidation correlate with the H-bonds in the starting diols.     

Eine neue Synthese von (±)-Dihydrorecifeiolid

A New Synthesis of (±)-Dihydrorecifeiolide Ethyl 1-(2′-formylethyl)-2-oxocyclooctane-1-carboxylate ( 2 ) prepared by Michael reaction of ethyl 2-oxocyclooctane-1-carboxylate ( 1 ) was regioselectively methylated at the aldehyde group with (CH₃)₂Ti[OCH(CH₃)₂]₂ to give 3 (Scheme 1). The alcohol 3 was treated with Bu₄NF to give the deethoxycarbonylated product 4 which by distillation gave the bicyclic enol ether 5 . Oxidation (m-chloroperbenzoic acid) of 5 and reduction of the resulting oxolacton 6 yielded the title compound (±)-dihydrorecifeiolide ( 7 ) in an overall yield of nearly 50 %. Methylation of the aldehyde 2 with MeLi gave the ring-enlarged lacton 9 in poor yield (13 %). The deethoxycarbonylation reaction 3 → 4 was studied in more detail (Scheme 3).     

Theoretical study of the mechanism of CH2CO + CN reaction

The potential energy surface information of the CH₂CO + CN reaction is obtained at the B3LYP/6‐311+G(d,p) level. To gain further mechanistic knowledge, higher‐level single‐point calculations for the stationary points are performed at the QCISD(T)/6‐311++G(d,p) level. The CH₂CO + CN reaction proceeds through four possible mechanisms: direct hydrogen abstraction, olefinic carbon addition–elimination, carbonyl carbon addition–elimination, and side oxygen addition–elimination. Our calculations demonstrate that R→IM1→TS3→P3: CH₂CN + CO is the energetically favorable channel; however, channel R→IM2→TS4→P4: CH₂NC + CO is considerably competitive, especially as the temperature increases (R, IM, TS, and P represent reactant, intermediate, transition state, and product, respectively). The present study may be helpful in probing the mechanism of the CH₂CO + CN reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Are the anions MeO(CO) (n = 1 and 2) methoxide anion donors in the gas phase? A theoretical investigation

• 1. The anions CH₃O‐^–CO and CH₃OCO‐^–CO are both methoxide anion donors. The processes CH₃O‐^–CO → CH₃O^– + CO and CH₃OCO—CO → CH₃O^– + 2CO have ΔG values of +8 and ?68 kJ mol^?1, respectively, at the CCSD(T)/6‐311++G(2d, 2p)//B3LYP/6‐311++G(2d,2p) level of theory.
• 2. The reactions CH₃OCOCO → CH₃OCO + CO (ΔG = ?22 kJ mol^?1) and CH₃COCH(O^–)CO₂CH₃ → CH₃COCH(O^–)OCH₃ + CO (ΔG = +19 kJ mol^?1) proceed directly from the precursor anions via the transition states (CH₃OCO…CO₂)^– and (CH₃COCHO…CH₃OCO)^–, respectively.
• 3. Anion CH₃COCH(O^–)CO₂CH₃ undergoes methoxide anion transfer and loss of two molecules of CO in the reaction sequence CH₃COCH(O^–)CO₂CH₃ → CH₃CH(O^–)COCO₂CH₃ → [CH₃CHO (CH₃OCO‐^–CO)] → CH₃CH(O^–)OCH₃ + 2CO (ΔG = +9 kJ mol^?1). The hydride ion transfer in the first step is a key feature of the reaction sequence.

Copyright © 2010 John Wiley & Sons, Ltd.     

Dibenz [b,f]-1, 4-oxazepin-11 (10 H)-one und Dibenz [b,e]-1, 4-oxazepin-11 (5 H)-one. 12. Mitteilung über siebengliedrige Heterocyclen

The syntheses of dibenzo [b, f]-1, 4-oxazepin-11 (10 H)-ones (I) with electron-attracting substituents in position 2 by ring closure of the sodium salts of 2-halogeno-2′-hydroxy-benzanilides (II) are described. The reaction of II (R = SO₂·N(CH₃)₂) in N-methylpyrrolidone also led, by SMILES rearrangement, to the isomeric minor product dibenzo [b, e]-1, 4-oxazepin-11 (5 H)-one (III; R = SO₂·N(CH₃)₂), whose constitution was proven by synthesis from VI. In the case of II (R = SO₂·CH₃), the 5-methylsulfonyl-2-(2-hydroxyanilino)-benzoic acid (VI; R = SO₂·CH₃) was obtained directly after hydrolysis. The lactam I (R = NO₂) was rearranged to the corresponding acid VI by heating with dilute caustic soda.