14915-25-4Relevant academic research and scientific papers
A model reaction assesses contribution of H-tunneling and coupled motions to enzyme catalysis
Liu, Qi,Zhao, Yu,Hammann, Blake,Eilers, James,Lu, Yun,Kohen, Amnon
, p. 6825 - 6833 (2012)
To assess the contribution of physical features to enzyme catalysis, the enzymatic reaction has to be compared to a relevant uncatalyzed reaction. While such comparisons have been conducted for some hydrolytic and radical reactions, it is most challenging for biological hydride transfer and redox reactions in general. Here, the same experimental tools used to study the H-tunneling and coupled motions for enzymatic hydride transfer between two carbons were used in the study of an uncatalyzed model reaction. The enzymatic oxidations of benzyl alcohol and its substituted analogues mediated by alcohol dehydrogenases were compared to the oxidations by 9-phenylxanthylium cation (PhXn+). The PhXn+serves as an NAD+ model, while the solvent, acetonitrile, models the protein environment. Experimental comparisons included linear free energy relations with Hammett reaction constant (ρ) of zero versus -2.7; temperature-independent versus temperature-dependent primary KIEs; deflated secondary KIEs with deuteride transfer (i.e., primary-secondary coupled motion) versus no coupling between secondary KIEs and H- or D-transfer; and large versus small secondary KIEs for the enzymatic versus uncatalyzed alcohol oxidation. Some of the differences may come from differences in the order of microscopic steps between the catalyzed versus uncatalyzed reactions. However, several of these comparative experiments indicate that in contrast to the uncatalyzed reaction the transition state of the enzymatic reaction is better reorganized for H-tunneling and its H-donor is better rehybridized prior to the C-H→C transfer. These findings suggest an important role for these physical features in enzyme catalysis.
Palladium-Catalyzed Three-Component Silylalkoxylation of 1,3-Diene with Alcohol and Disilane via Oxidative Coupling
Torii, Kazuyuki,Tabaru, Kazuki,Obora, Yasushi
, p. 4898 - 4902 (2021)
A regioselective and Z-selective three-component silylalkoxylation of 1,3-diene using various alcohols, disilane, and a catalytic Pd/Cu/1,4-benzoquinone/O2 system is established in this Letter. The reaction generates tetra-substituted allyl silanes containing allyl ether moieties in up to 80% isolated yield and on a 1-10 mmol scale via oxidative coupling. A wide variety of substrates, including benzyl alcohol derivates, aliphatic alcohols, and bioactive compounds such as cholesterol, are suitable for use in the developed reaction system.
Electron and Hydrogen Atom Transfer Mechanisms for the Photoreduction of o-Quinones. Visible Light Induced Photoreaction of β-Lapachone with Amines, Alcohols, and Amino Alcohols
Ci, Xiaohong,Silva, Rosaly Silveira da,Nicodem, David,Whitten, David G.
, p. 1337 - 1343 (1989)
β-Lapachone (1), a substituted o-naphthoquinone absorbing into the visible (λmax=424 nm in benzene), is cleanly and efficiently reduced to the corresponding semiquinone radical upon photolysis in degassed solutions with alcohols, amines, and β-amino alcohols.The course and products of these photoreactions have been followed by NMR, ESR, fluorescence, and absorption spectroscopy.For all three types of reductant the overall reaction involves 2e- oxidation of the donor, and the quantum efficiencies show a dependence upon quinone concentration indicative of therole of a second dark reduction of 1 by products of the primary photolysis.For amines and amino alcohols the reaction is initiated by single electron transfer quenching of triplet 1.For triethylamine the mechanism is indicated to be a sequence of two electron transfer-proton transfer steps culminating in two semiquinone radicals and the enamine Et2NCH=CH2.For amino alcohols a C-C cleavage concurrent with deprotonation of the alcohol (oxidative photofragmentation) occurs, in competition with reverse electron transfer, following the quenching step.For both amines and amino alcohols, limiting efficiencies of reaction approach 2 (for QH. formation).In contrast, both 2-propanol and benzyl alcohol are oxidized by excited states of 1 with much lower efficiency.The probable mechanism for photooxidation of the alcohols involves a H atom abstraction quenching of the excited state followed by an electron transfer-proton transfer sequence in which a ground-state 1 is reduced.Lower limiting efficiencies for photoreduction of 1 by the alcohols are attributed to inefficiencies of net H-atom transfer in the quenching step.
Are carboxyl groups the most acidic sites in amino acids? Gas-phase acidity, H/D exchange experiments, and computations on cysteine and its conjugate base
Tian, Zhixin,Pawlow, Anna,Poutsma, John C.,Kass, Steven R.
, p. 5403 - 5407 (2007)
Hydrogen-deuterium exchange experiments were carried out on the conjugate base of cysteine with four different deuterated alcohols. Three H/D exchanges are observed to take place in each case, and a relay mechanism which requires the SH and CO2
Critical role of solvent-modulated hydrogen-binding strength in the catalytic hydrogenation of benzaldehyde on palladium
Cheng, Guanhua,Chin, Ya-Huei (Cathy),Gutiérrez, Oliver Y.,Jentys, Andreas,Lercher, Johannes A.,Liu, Yue
, p. 976 - 985 (2021/11/24)
Solvents not only disperse reactants to enhance mass transport in catalytic reactions but also alter the reaction kinetically. Here, we show that the rate of benzaldehyde hydrogenation on palladium differs by up to one order of magnitude in different solv
A Water/Toluene Biphasic Medium Improves Yields and Deuterium Incorporation into Alcohols in the Transfer Hydrogenation of Aldehydes
Ruiz-Casta?eda, Margarita,Santos, Lucía,Manzano, Blanca R.,Espino, Gustavo,Jalón, Félix A.
supporting information, p. 1358 - 1372 (2021/03/16)
Deuterium labeling is an interesting process that leads to compounds of use in different fields. We describe the transfer hydrogenation of aldehydes and the selective C1 deuteration of the obtained alcohols in D2O, as the only deuterium source. Different aromatic, alkylic and α,β-unsaturated aldehydes were reduced in the presence of [RuCl(p-cymene)(dmbpy)]BF4, (dmbpy=4,4′-dimethyl-2,2′-bipyridine) as the pre-catalyst and HCO2Na/HCO2H as the hydrogen source. Moreover, furfural and glucose, were selectively reduced to the valuable alcohols, furfuryl alcohol and sorbitol. The processes were carried out in neat water or in a biphasic water/toluene system. The biphasic system allowed easy recycling, higher yields, and higher selective D incorporation (using D2O/toluene). The deuteration took place due to an efficient effective M–H/D+ exchange from D2O that allows the inversion of polarity of D+ (umpolung). DFT calculations that explain the catalytic behavior in water are also included.
Cross β-arylmethylation of alcohols catalysed by recyclable Ti-Pd alloys not requiring pre-activation
Utsunomiya, Masayoshi,Kondo, Ryota,Oshima, Toshinori,Safumi, Masatoshi,Suzuki, Takeyuki,Obora, Yasushi
supporting information, p. 5139 - 5142 (2021/05/31)
Ti-Pd alloy catalysts were developed for the cross β-arylmethylation between arylmethylalcohols and different primary alcohols via a hydrogen autotransfer mechanism. The alloy catalysts could be reused multiple times without the need for pre-activation. Analysis of the reaction solution by inductively coupled plasma atomic absorption spectroscopy indicated that only a minimal amount of Ti and no Pd was leached from the catalyst.
Dehydrogenative Coupling of Aldehydes with Alcohols Catalyzed by a Nickel Hydride Complex
Eberhardt, Nathan A.,Wellala, Nadeesha P. N.,Li, Yingze,Krause, Jeanette A.,Guan, Hairong
, p. 1468 - 1478 (2019/04/17)
A nickel hydride complex, {2,6-(iPr2PO)2C6H3}NiH, has been shown to catalyze the coupling of RCHO and R′OH to yield RCO2R′ and RCH2OH, where the aldehyde also acts as a hydrogen acceptor and the alcohol also serves as the solvent. Functional groups tolerated by this catalytic system include CF3, NO2, Cl, Br, NHCOMe, and NMe2, whereas phenol-containing compounds are not viable substrates or solvents. The dehydrogenative coupling reaction can alternatively be catalyzed by an air-stable nickel chloride complex, {2,6-(iPr2PO)2C6H3}NiCl, in conjunction with NaOMe. Acids in unpurified aldehydes react with the hydride to form nickel carboxylate complexes, which are catalytically inactive. Water, if present in a significant quantity, decreases the catalytic efficiency by forming {2,6-(iPr2PO)2C6H3}NiOH, which causes catalyst degradation. On the other hand, in the presence of a drying agent, {2,6-(iPr2PO)2C6H3}NiOH generated in situ from {2,6-(iPr2PO)2C6H3}NiCl and NaOH can be converted to an alkoxide species, becoming catalytically competent. The proposed catalytic mechanism features aldehyde insertion into the nickel hydride as well as into a nickel alkoxide intermediate, both of which have been experimentally observed. Several mechanistically relevant nickel species including {2,6-(iPr2PO)2C6H3}NiOC(O)Ph, {2,6-(iPr2PO)2C6H3}NiOPh, and {2,6-(iPr2PO)2C6H3}NiOPh·HOPh have been independently synthesized, crystallographically characterized, and tested for the catalytic reaction. While phenol-containing molecules cannot be used as substrates or solvents, both {2,6-(iPr2PO)2C6H3}NiOPh and {2,6-(iPr2PO)2C6H3}NiOPh·HOPh are efficient in catalyzing the dehydrogenative coupling of PhCHO with EtOH.
Selective oxidation of exogenous substrates by a bis-Cu(III) bis-oxide complex: Mechanism and scope
Large, Tao A.G.,Mahadevan, Viswanath,Keown, William,Stack, T. Daniel P.
, p. 782 - 792 (2019/01/03)
Cu(III)2(μ-O)2 bis-oxides (O) form spontaneously by direct oxygenation of nitrogen-chelated Cu(I) species and constitute a diverse class of versatile 2e?/2H+ oxidants, but while these species have attracted attention as biomimetic models for dinuclear Cu enzymes, reactivity is typically limited to intramolecular ligand oxidation, and systems exhibiting synthetically useful reactivity with exogenous substrates are limited. OTMPD (TMPD = N1, N1, N3, N3-tetramethylpropane-1,3-diamine) presents an exception, readily oxidizing a diverse array of exogenous substrates, including primary alcohols and amines selectively over their secondary counterparts in good yields. Mechanistic and DFT analyses suggest substrate oxidation proceeds through initial axial coordination, followed by rate-limiting rotation to position the substrate in the Cu(III) equatorial plane, whereupon rapid deprotonation and oxidation by net hydride transfer occurs. Together, the results suggest the selectivity and broad substrate scope unique to OTMPD are best attributed to the combination of ligand flexibility, limited steric demands, and ligand oxidative stability. In keeping with the absence of rate-limiting C–H scission, OTMPD exhibits a marked insensitivity to the strength of the substrate Cα–H bond, readily oxidizing benzyl alcohol and 1-octanol at near identical rates.
Iron-Catalyzed Ligand Free α-Alkylation of Methylene Ketones and β-Alkylation of Secondary Alcohols Using Primary Alcohols
Alanthadka, Anitha,Bera, Sourajit,Banerjee, Debasis
, p. 11676 - 11686 (2019/10/02)
Herein, we demonstrate a general and broadly applicable catalytic cross coupling of methylene ketones and secondary alcohols with a series of primary alcohols to disubstituted branched ketones. A simple and nonprecious Fe2(CO)9 catalyst enables one-pot oxidations of both primary and secondary alcohols to a range of branched gem-bis(alkyl) ketones. A number of bond activations and formations selectively occurred in one pot to provide the ketone products. Coupling reactions can be performed in gram scale and successfully applied in the synthesis of an Alzehimer's drug. Alkylation of a steroid hormone can be achieved. A single catalyst enables sequential one-pot double alkylation to bis-hetero aryl ketones using two different alcohols. Preliminary mechanistic studies using an IR probe, deuterium labeling, and kinetic experiments established the participation of a borrowing-hydrogen process using Fe catalyst, and the reaction produces H2 and H2O as byproducts.
