Theoretical study on the mechanism of reaction between 3‐hydroxy‐3‐methyl‐2‐butanone and malononitrile catalyzed by magnesium ethoxide

The mechanism of reaction between 3‐hydroxy‐3‐methyl‐2‐butanone and malononitrile for the synthesis of 2‐dicyanomethylene‐4,5,5‐trimethyl‐2,5‐dihydrofuran‐3‐carbonitrile catalyzed by magnesium ethoxide was investigated by density functional theory (DFT). The geometries and the frequencies of reactants, intermediates, transition states, and products were calculated at the B3LYP/6–31G(d) level. The vibration analysis and the IRC analysis demonstrated the authenticity of transition states, and the reaction processes were confirmed by the changes of charge density at bond‐forming critical point. The results indicated that magnesium ethoxide is an effective catalyst in the synthesis of 2‐dicyanomethylene‐4,5,5‐trimethyl‐2,5‐dihydrofuran‐3‐carbonitrile from malononitrile and 3‐hydroxy‐3‐methyl‐2‐butanone. The activation energy of reaction with magnesium ethoxide decreased by 102.37 kJ mol^?1 compared with that of the reaction without it. The mechanism of reaction with catalyst magnesium ethoxide differs from that of reaction without it. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 227–235, 2009     

Bismuth halide‐catalyzed polymerizations of ε‐caprolactone

In contrast to BiF₃, the other three Bi‐halides catalyzed the ring‐opening polymerization of ε‐caprolactone (ε‐CL) in bulk. A temperature of 140 °C was found to be advantageous for rapid polymerization and optimum molecular weights. At this temperature, the reactivity of the catalysts increases in the order BiCl₃ < BiBr₃ < BiJ₃. Variation of the monomer‐catalyst ratio (M/C) yielded number‐average molecular weights (M_ns) up to 80,000 Da (corrected SEC data, 120,000 Da uncorrected), but a proper control of the M_ns was not achieved. In addition to CH₂? OH endgroups, CH₂Cl, CH₂Br, and CH₂J endgroups were detected, but no evidence for a cationic polymerization mechanism was found. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7483–7490, 2008     

5α‐Androst‐3‐en‐17‐one oxime

The title compound, C₁₉H₂₉NO, is a C17‐oxime derivative of a potent aromatase inhibitor, which surprisingly has been found to have no inhibitory power. It crystallizes with two independent molecules in the asymmetric unit. C=N—O—H...N hydrogen bonds link pairs of molecules to form dimers almost parallel to the bc plane. Cohesion of the structure is also due to another three C—H...O hydrogen bonds directed along the a axis. This hydrogen‐bonding scheme can be correlated to the almost complete loss of inhibitory power of the title compound.     

The Structures of Indazolin‐3‐one (=1,2‐Dihydro‐3H‐indazol‐3‐one) and 7‐Nitroindazolin‐3‐one

The existence of polymorphism in parent indazolin‐3‐one (=1,2‐dihydro‐3H‐indazol‐3‐one; 1 ) is reported as well as an X‐ray and NMR CPMAS study establishing that its 7‐nitro derivative 2 exists as the 3‐hydroxy tautomer. Absolute shieldings calculated at the GIAO/B3LYP/6‐311++G(d,p) level were used to determine the tautomeric oxo/hydroxy equilibrium in solution, i.e., always the 1H‐indazol‐3‐ol tautomer predominates.     

Tautomerism of 3‐nitro‐1,2,4‐triazole‐5‐one radical anions

The non‐degenerate tautomers of 3‐nitro‐1,2,4‐triazole‐5‐one (NTO) radical anions were investigated for the first time by an ESR method during electrochemical reduction of NTO in an aprotic medium. Copyright © 2009 John Wiley & Sons, Ltd.     

Theoretical study on the mechanism of reaction between 3-hydroxy-3-methyl-2-butanone and malononitrile catalyzed by lithium ethoxide

The The mechanism of reaction between 3-hydroxy-3-methyl-2-butanone and malononitrile for the synthesis of 2-dicyanomethylene-4, 5, 5-trimethyl-2,5-dihydrofuran-3-carbonitrile catalyzed by lithium ethoxide was investigated by density functional theory (DFT). The geometries and the frequencies of reactants, intermediates, transition states and products were calculated at the B3LYP/6-31G(d) level. The vibration analysis and the IRC analysis verified the authenticity of transition states. The reaction processes were confirmed by the changes of charge density at the bond-forming critical point. The results indicated that lithium ethoxide is an effective catalyst in the synthesis of 2-dicyanomethylene-4, 5, 5-trimethyl-2, 5-dihydrofuran-3-carbonitrile from malononi-trile and 3-hydroxy-3-methyl-2-butanone. The activation energy of the reaction with lithium ethoxide was 115.86 kJ·mol⁻¹ less than the uncatalyzed reaction. The mechanism of the lithium ethoxide catalyzed reaction differed from the mechanism of the uncatalyzed reaction.     

Synthesis of block and end‐functionalized polyesters by triflimide‐catalyzed ring‐opening polymerization of ε‐caprolactone, 1,5‐dioxepan‐2‐one,and rac‐lactide

The ring‐opening polymerization (ROP) of cyclic esters, such as ε‐caprolactone, 1,5‐dioxepan‐2‐one, and racemic lactide using the combination of 3‐phenyl‐1‐propanol as the initiator and triflimide (HNTf₂) as the catalyst at room temperature with the [monomer]₀/[initiator]₀ ratio of 50/1 was investigated. The polymerizations homogeneously proceeded to afford poly(ε‐caprolactone) (PCL), poly(1,5‐dioxepan‐2‐one) (PDXO), and polylactide (PLA) with controlled molecular weights and narrow polydispersity indices. The molecular weight determined from an ¹H NMR analysis (PCL, M_n,NMR = 5380; PDXO, M_n,NMR = 5820; PLA, M_n,NMR = 6490) showed good agreement with the calculated values. The ¹H NMR and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry analyses strongly indicated that the obtained compounds were the desired polyesters. The kinetic measurements confirmed the controlled/living nature for the HNTf₂‐catalyzed ROP of cyclic esters. A series of functional alcohols, such as propargyl alcohol, 6‐azido‐1‐hexanol, N‐(2‐hydroxyethyl)maleimide, 5‐hexen‐1‐ol, and 2‐hydroxyethyl methacrylate, successfully produced end‐functionalized polyesters. In addition, poly(ethylene glycol)‐block‐polyester, poly(δ‐valerolactone)‐block‐poly(ε‐caprolactone), and poly(ε‐caprolactone)‐block‐polylactide were synthesized using the HNTf₂‐catalyzed ROP. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2455–2463     

Ring‐opening polymerization of lactide, ε‐caprolactone and their copolymerization catalyzed by β‐diketiminate zinc complexes

A series of zinc silylamido complexes bearing non‐symmetric β ‐diketiminate ligands were synthesized and structurally characterized. Ring‐opening polymerization (ROP) of rac ‐lactide catalyzed by these zinc complexes afforded heterotactic polylactides at room temperature (P _r = 0.79 ~ 0.83 in THF). The steric and electronic characteristics of the ancillary ligands showed significant influence on the polymerization performance of the corresponding zinc complexes. All these zinc complexes also showed moderate activities toward the polymerization of ε ‐caprolactone at ambient temperature in toluene, producing polycaprolactones (PCLs) with high molecular weights and moderate polydispersities. PCL‐b ‐PLLA copolymers could be obtained via three different copolymerization strategies (one‐pot polymerization, and sequential addition of the two monomers in either order) by adopting complex 6 as the initiator through the adjustment of reaction temperatures. The diblock nature of the copolymers was confirmed by ¹³C NMR spectroscopy and DSC analysis.     

Computational study of the catalytic synthesis of 5‐nitro‐1,2,4‐triazol‐3‐one

In this study, 5‐nitro‐1,2,4‐triazol‐3‐one (NTO) was theoretically synthesized from urea via chlorination followed by amination, formylation, and nitration under aqueous and gaseous environments based on experience of experimental methods, and metal chlorides and metal oxides were used as catalysts to promote reaction. Reaction routes closely related to experimental processes were successfully constructed, and the corresponding energy barriers were estimated for each elementary reaction. Reaction conditions distinct from those reported in the literature (including the adoption of aluminum chloride, ferric chloride, aluminum oxide, ferrous oxide, and chromium oxide catalysts, the use of nitric acid and dinitrogen pentoxide as nitration agents, and adjustment of the reaction temperature) were used in corresponding reaction systems, and the modeling results suggested that ferric chloride is a good catalyst for the chlorination reaction, ferrous oxide is suitable for catalyzing amination, formylation, and nitration, and nitric acid is the better agent for nitration. Estimates of the comparable energy barriers for each reaction stage were considered to imply more feasible pathways for NTO synthesis. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Crosslinking study of mixtures of DGEBA and 1,3‐dioxan‐2‐one catalyzed by lanthanide triflates

Ytterbium and lanthanum triflates were used as catalysts to cure diglycidylether of bisphenol A with different proportions of 1,3‐dioxan‐2‐one. The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing process. We observed the formation of a five‐membered cyclic carbonate that remains unreacted at the chain ends, because of an equilibrium process between the spiroorthocarbonates that had formed as intermediate species. The kinetics were studied by DSC experiments and analyzed with isoconversional procedures. The system catalyzed by ytterbium triflate had a higher curing rate. Thermogravimetric analysis and dynamic mechanical thermal analysis experiments were used to evaluate the properties of the materials obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5799–5813, 2005     

Base catalyzed isomerization of epoxides. I. The isomerization of β-chloroepoxides

The base catalyzed isomerizations of epichlorohydrin, 1-chloro-2,3-epoxy-2-methylpropane, 1-chloro-2,3-epoxybutane, and 3-chloro-1,2-epoxybutane have been studied, using lithium ortho-phosphate as the basic catalyst. Chloroketones and dichloro-alcohols are the major products. This is the first example of a compound with an electron withdrawing group attached to the carbon atom adjacent to the oxirane ring which undergoes the α-elimination pathway. A bidirectional mechanism is proposed to explain the experimental results. The stereochemistry of the hydrochlorination of 1-chloro-2,3-epoxybutane and 3-chloro-1,2-epoxybutane has also been studied.     

Palladium‐catalyzed dehalogenation of 5‐halopyrazoles

A new and efficient method for the dehalogenation of 5‐halopyrazoles was developed by using the catalytic amount of palladium (II) chloride and triphenylphosphine as a ligand at reflux under constant flow of hydrogen gas. The reaction gave the corresponding pyrazole products in good to excellent yields (≥83%). J. Heterocyclic Chem., (2012).     

Quantum chemical modeling of 1,1‐proton transfer reaction catalyzed by a cofactor‐independent α‐methylacyl‐CoA racemase

α‐Methylacyl‐CoA racemases (AMACR) are essential enzymes for branched‐chain lipids and drugs metabolism. AMACR catalyzes the chiral inversion of (2R) and (2S)‐methylacyl‐CoA esters in both directions. In this study, we investigated the catalytic mechanism of Mycobacterium tuberculosis (MCR) α‐methylacyl‐CoA racemase by using the density functional theory with the hybrid functional B3LYP. Our calculations elucidate and support the mechanism proposed by Prasenjit Bhaumik. His126 and Asp156 serve as the acid/base‐pair residues in the 1,1‐proton transfer catalytic reaction. From the optimized structures, it can be seen that an enolate intermediate is formed and the possibility of forming a ketene or a carbanion intermediate is excluded. By comparing the energy barriers, we could consider that the deprotonation step is the rate‐determined step in the invert direction from (S)‐ to (R)‐enantiomer. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Synthesis of the Natural Product Building Block 5‐(3‐Bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one and its Chiral Characterization by Using Chiroptical Spectroscopy

The absolute configuration of 5‐(3‐bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one, an intermediate in the synthesis of various natural products, is assigned by using vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD). Experimental spectra were compared to density functional theory (DFT) calculations of the molecule with known configuration. These three techniques independently confirm that the absolute configuration is (S)‐5‐(3‐bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one, thus enabling us to assign the absolute configuration with high reliability. The reliability of the VCD analysis was assessed quantitatively by using the CompareVOA program. We found that, in cases in which the agreement between theory and experiment was very good, a value of 10 cm^?1 for the triangular weighting function gave a more‐realistic discriminative power between enantiomers than the default value of 20 cm^?1.     

Reactions of 5‐methylene‐1,3‐thiazolidine‐2‐thione and 5‐methylene‐2‐oxazolidinone with isocyanates catalyzed by bases

5‐Methylene‐1,3‐thiazolidine‐2‐thione and 5‐methylene‐2‐oxazolidinone can react with isocyanates to give the corresponding condensed urethanes in high yields in the presence of organic or inorganic bases under mild reaction conditions. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:610–616, 2001     

Density functional theory study of the interaction between 3‐nitro‐1,2,4‐triazole‐5‐one and ammonia

Two fully optimized geometries of 3‐nitro‐1,2,4‐triazol‐5‐one (NTO)–NH₃ complexes have been obtained with the density function theory (DFT) method at the B3LYP/6‐311++G** level. The intermolecular interaction energy is calculated with zero point energy (ZPE) correction and basis set superposition error (BSSE) correction. The greatest corrected intermolecular interaction of the NTO–NH₃ complexes is ?37.58 kJ/mol. Electrons in complex systems transfer from NH₃ to NTO. The strong hydrogen bonds contribute to the interaction energies dominantly. Natural bond orbital (NBO) analysis is performed to reveal the origin of the interaction. Based on vibrational analysis, the changes of thermodynamic properties from the monomer to complexes with the temperature ranging from 200 K to 800 K have been obtained using the statistical thermodynamic method. It is found that two NTO–NH₃ complexes can be produced spontaneously from NTO and NH₃ at normal temperature. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Shock‐tube spectroscopic water measurements and detailed kinetics modeling of 1‐pentene and 3‐methyl‐1‐butene

To understand the effects of the chemical structure of two C₅ alkene isomers on their combustion properties, and to highlight the major chemical reactions occurring during their high‐temperature oxidation, water time histories were measured behind reflected shock waves for the oxidation of 1‐pentene (C₅H₁₀‐1) and 3‐methyl‐1‐butene (3M1B) in 99.5% Ar. The experiments were carried out at three different equivalence ratios (φ = 0.5, 1.0, and 2.0) at pressures and temperatures ranging from 1.29 to 1.47 atm and 1 331 to 1 877 K, respectively. The H₂O quantification extends the database for 1‐pentene and provides new insights for 3M1B. These unique results were used to validate and to develop a new detailed kinetics model. Numerical predictions are presented, and the new model was able to capture the results with suitable accuracy, with 3M1B being notably more reactive than C₅H₁₀‐1. Sensitivity and rate‐of‐production analyses were performed to help explain the results. Under the present conditions, the reactivity is rapidly initiated by molecular dissociation of a fraction of the pentene isomers. The initiation phase then induces H‐atom abstraction by active radicals (H, OH, O, HO₂, and CH₃) to first produce alkenyl C₅H₉ radicals (or an alkyl radical and an alkenyl radical by breaking a C─C bond) and subsequent, smaller fragments. The difference in terms of reactivity between the isomers is essentially due to the fact that 3M1B has one particularly weak tertiary allylic C─H bond, which allows for fast H‐atom abstraction compared with 1‐pentene.     

An X‐ray crystallographic and density functional theory study of (3Z)‐4‐(5‐ethylsulfonyl‐2‐hydroxyanilino)pent‐3‐en‐2‐one and (3Z)‐4‐(5‐tert‐butyl‐2‐hydroxyanilino)pent‐3‐en‐2‐one

The Schiff base enaminones (3Z)‐4‐(5‐ethylsulfonyl‐2‐hydroxyanilino)pent‐3‐en‐2‐one, C₁₃H₁₇NO₄S, (I), and (3Z)‐4‐(5‐tert‐butyl‐2‐hydroxyanilino)pent‐3‐en‐2‐one, C₁₅H₂₁NO₂, (II), were studied by X‐ray crystallography and density functional theory (DFT). Although the keto tautomer of these compounds is dominant, the O=C—C=C—N bond lengths are consistent with some electron delocalization and partial enol character. Both (I) and (II) are nonplanar, with the amino–phenol group canted relative to the rest of the molecule; the twist about the N(enamine)—C(aryl) bond leads to dihedral angles of 40.5 (2) and −116.7 (1)° for (I) and (II), respectively. Compound (I) has a bifurcated intramolecular hydrogen bond between the N—H group and the flanking carbonyl and hydroxy O atoms, as well as an intermolecular hydrogen bond, leading to an infinite one‐dimensional hydrogen‐bonded chain. Compound (II) has one intramolecular hydrogen bond and one intermolecular C=O...H—O hydrogen bond, and consequently also forms a one‐dimensional hydrogen‐bonded chain. The DFT‐calculated structures [in vacuo, B3LYP/6‐311G(d,p) level] for the keto tautomers compare favourably with the X‐ray crystal structures of (I) and (II), confirming the dominance of the keto tautomer. The simulations indicate that the keto tautomers are 20.55 and 18.86 kJ mol⁻¹ lower in energy than the enol tautomers for (I) and (II), respectively.     

Competitive double bond isomerization kinetics of 1‐dodecene and 11‐dococene on Amberlyst® 15

We followed the concurrent double bond isomerizations of 1‐dodecene (C12 NAO) and 11‐dococene (C22 IO) on Amberlyst® 15 at 90°C, observing the movement of the double bond from the middle of a C22 chain to its end and the movement of the double bond from the end of a C12 chain to its middle. Double bond migration was stepwise for both chains, and the kinetics were consistent with a common isomerization rate for all olefins of the same chain length, regardless of location of the double bond. Internal dodecenes isomerized 1.35 times faster than internal dococenes, suggesting a higher adsorption coefficient for dodecenes than for dococenes onto Amberlyst® 15 at 90°C. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 745–752, 2012