Magnesium bistrifluoromethanesulfonimide as a new and efficient acylation catalyst

Magnesium bistrifluoromethanesulfonimide catalyzed the acetylation of phenols, alcohols, and thiols under solvent-free conditions at room temperature and in short times. Electron-deficient and sterically hindered phenols provided excellent yields. The catalyst was found to be general for acylation with other anhydrides, such as propionic, isobutyric, pivalic, chloroacetic, and benzoic anhydrides. The rate of acylation was influenced by the electronic and steric factors associated with the anhydride. The reaction with less electrophilic anhydrides (e.g., chloroacetic and benzoic anhydrides) required higher temperature (approximately 80 degrees C). Chemoselective acetylation, pivalation, and benzoylation took place with acid-sensitive alcohols without any competitive dehydration/rearrangement.     

The DMAP-catalyzed acetylation of alcohols--a mechanistic study (DMAP = 4-(dimethylamino)pyridine)

The acetylation of tert-butanol with acetic anhydride catalyzed by 4-(dimethylamino)pyridine (DMAP) has been studied at the Becke3 LYP/6-311 + G(d,p)//Becke3 LYP/6-31G(d) level of theory. Solvent effects have been estimated through single-point calculations with the PCM/UAHF solvation model. The energetically most favorable pathway proceeds through nucleophilic attack of DMAP at the anhydride carbonyl group and subsequent formation of the corresponding acetylpyridinium/acetate ion pair. Reaction of this ion pair with the alcohol substrate yields the final product, tert-butylacetate. The competing base-catalyzed reaction pathway can either proceed in a concerted or in a stepwise manner. In both cases the reaction barrier far exceeds that of the nucleophilic catalysis mechanism. The reaction mechanism has also been studied experimentally in dichloromethane through analysis of the reaction kinetics for the acetylation of cyclohexanol with acetic anhydride, in the presence of DMAP as catalyst and triethylamine as the auxiliary base. The reaction is found to be first-order with respect to acetic anhydride, cyclohexanol, and DMAP, and zero-order with respect to triethyl amine. Both the theoretical as well as the experimental studies strongly support the nucleophilic catalysis pathway.     

醇在钒基催化剂上的氧化

以过氧化叔丁醇作为氧化剂,研究了醇类(苯甲醇、1-苯基乙醇和环己醇)在钒基催化剂上的氧化反应.制备了含苯磷二酚配体或吡嗪-2-羧酸酯配体的钒配合物,并运用傅里叶变换红外光谱、核磁共振谱、紫外-可见光谱及元素分析对其进行了表征.考察了溶剂对该类反应的影响.发现在甲苯溶剂中进行氧化反应时,苯甲醇被氧化成苯甲醛而不会被深度氧化为苯甲酸;而在乙腈溶剂中,苯甲醛和苯甲酸均有生成.此外,对不同钒磷氧化物的催化活性进行了比较,结果表明,在乙腈溶剂中的产品收率比在甲苯溶剂中高.     

A C=O⋅⋅⋅Isothiouronium Interaction Dictates Enantiodiscrimination in Acylative Kinetic Resolutions of Tertiary Heterocyclic Alcohols

A combination of experimental and computational studies have identified a C=O???isothiouronium interaction as key to efficient enantiodiscrimination in the kinetic resolution of tertiary heterocyclic alcohols bearing up to three potential recognition motifs at the stereogenic tertiary carbinol center. This discrimination was exploited in the isothiourea‐catalyzed acylative kinetic resolution of tertiary heterocyclic alcohols (38 examples, s factors up to >200). The reaction proceeds at low catalyst loadings (generally 1 mol %) with either isobutyric or acetic anhydride as the acylating agent under mild conditions.     

Kinetics of oxidation of organic compounds by silver(II) in aqueous perchloric acid solution. Part 5

Summary The kinetics and mechanism of oxidation of a series of alcohols, namely cyclohexanol, cyclopentanol, pentan-2-ol and benzyl alcohol, by silver(II) perchlorate in perchloric acid solution. have been investigated by the stopped-flow technique. These oxidations proceed through two parallel pathways involving Ag²⁺ and AgOH⁺ species. In the case of benzyl alcohol, the hydroxo species, which has been found to be almost universally reactive toward different organic substrates, is inactive; this behaviour has been interpreted in terms of interaction of the oxidant with the aromatic moiety in the alcohol. The reactivities are discussed in terms of substrate reaction sites with reference to electronic availability and reaction products.     

（R）—N—乙酰四氢噻唑—2—硫酮—4—羧酸与醇的反应

（Ｒ）－Ｎ－乙酰四氢噻唑－２－硫酮－４－羧酸与醇反应，在ＳＯＣｌ２存在下得到乙酸酯及四氢噻唑－２－硫酮－４－羧酸酯；在碳酸钾存在下得到乙酸酯及四氢噻唑－２－硫酮－４－羧酸；在二环己基碳二亚胺（ＤＣＣ）存在下得到缩水产物Ｎ－乙酰四氢噻唑－２－硫酮－４－羧酸酯。     

Flash photolytic generation of ortho-quinone methide in aqueous solution and study of its chemistry in that medium

Flash photolysis of o-hydroxybenzyl alcohol, o-hydroxybenzyl p-cyanophenyl ether, and (o-hydroxybenzyl)trimethylammonium iodide in aqueous perchloric acid and sodium hydroxide solutions, and in acetic acid and biphosphate ion buffers, produced o-quinone methide as a short-lived transient species that underwent hydration back to benzyl alcohol in hydrogen-ion catalyzed (k(H+) = 8.4 x 10(5) M(-1) s(-1)) and hydroxide-ion catalyzed (k(HO)- = 3.0 x 10(4) M(-1) s(-1)) reactions as well as an uncatalyzed (k(UC) = 2.6 x 10(2) s(-1)) process. The hydrogen-ion catalyzed reaction gave the solvent isotope effect k(H+)/k(D)+ = 0.42, whose inverse nature indicates that this process occurs by rapid and reversible equilibrium protonation of the carbonyl oxygen atom of the quinone methide, followed by rate-determining capture of the carbocation so produced by water. The magnitude of the rate constant of the uncatalyzed reaction, on the other hand, indicates that this process occurs by simple nucleophilic addition of water to the methylene group of the quinone methide. Decay of the quinone methide is also accelerated by acetic acid buffers through both acid- and base-catalyzed pathways, and quantitative analysis of the reaction products formed in these solutions shows that this acceleration is caused by nucleophilic reactions of acetate ion rather than by acetate ion assisted hydration. Bromide and thiocyanate ions also accelerate decay of the quinone methide through both hydrogen-ion catalyzed and uncatalyzed pathways, and the inverse nature of solvent isotope effects on the hydrogen-ion catalyzed reactions shows that these reactions also occur by rapid equilibrium protonation of the quinone methide carbonyl oxygen followed by rate-determining nucleophilic capture of the ensuing carbocation. Assignment of an encounter-controlled value to the rate constant for the rate-determining step of the thiocyanate reaction leads to pK(a) = -1.7 for the acidity constant of the carbonyl-protonated quinone methide.     

Simple synthesis of beta-D-glycopyranosides using beta-glycosidase from almonds

Enzymatic glycosidation of twenty-one kinds of alcohols (n-hepanol, n-octanol, 2-phenylethanol, 3-phenylpropanol, 4-phenylbutanol, 5-phenylpentanol, 6-phenylhexanol, furfury alcohol, 2-pyridinemethanol, isobutanol, isopentanol, p-methoxycinnamylalcohol) including secondary alcohols (isopropanol, cyclohexanol, 1-phenylethanol) and 1,omega-alkanediols (1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol), salicyl alcohol and 4-nitrophenyl beta-D-glucopyranoside (5) using beta-glucosidase from almonds stereoselectively gave the corresponding beta-D-glucopyranosides in moderate yield.     

Interaction of 2,2,6,6-tetramethylpiperidine-1-oxyl chloritewith alcohols

The kinetics of the oxidation of a series of alcohols (viz., ethanol, propan-2-ol, butan-1-ol, butan-2-ol, heptan-4-ol, decan-2-ol, propan-1,3-diol, butan-2,3-diol, cyclohexanol, benzyl alcohol, and borneol) with the oxoammonium salt 2,2,6,6-tetramethylpiperidine-1-oxyl chlorite in acetonitrile was studied by spectrophotometry. The products of oxidation of primary alcohols are the corresponding aldehydes and carboxylic acids, and the products of oxidation of secondary alcohols are ketones. The reaction rate is described by the second order equation. The rate constants and activation parameters were determined. The rate constant as a function of the alcohol nature is described by the one-parameter Taft equation.     

Gas-chromatographic determination of carboxylic acid anhydrides in oxidation products of alcohols and other organic compounds

A procedure was developed for the gas-chromatographic determination of carboxylic acid anhydrides in the composition of oxidation products of organic compounds after their conversion into alkyl formate by formic acid and benzyl alcohol or other primary alcohol introduced into the reaction medium. The reaction proceeds through the mixed anhydride, which is formed in situ from formic acid and the determined anhydride and is predominantly transformed into the corresponding alkyl formate in alcoholysis with alcohol. The potentialities of the procedure were illustrated by the determination of anhydrides in oxidation products of cyclohexane, cyclohexanone, and cyclohexanol.     

Highly powerful and practical acylation of alcohols with acid anhydride catalyzed by Bi(OTf)(3).

Bi(OTf)(3)-catalyzed acylation of alcohols with acid anhydride was evaluated in comparison with other acylation methods. The Bi(OTf)(3)/acid anhydride protocol was so powerful that sterically demanding or tertiary alcohols could be acylated smoothly. Less reactive acylation reagents such as benzoic and pivalic anhydride are also activated by this catalysis. In these cases, a new technology was developed in order to overcome difficulty in separation of the acylated product from the remaining acylating reagent: methanolysis of the unreacted anhydride into easily separable methyl ester realized quite easy separation of the desired acylation product. The Bi(OTf)(3)/acid anhydride protocol was applicable to a wide spectrum of alcohols bearing various functionalities. Acid-labile THP- or TBS-protected alcohol, furfuryl alcohol, and geraniol could be acylated as well as base-labile alcohols. Even acylation of functionalized tertiary alcohols was effected at room temperature.     

功能化离子液体[bmim]OTs催化乙酰化反应

以离子液体1-丁基-3-甲基咪唑四氟硼酸盐([bmim]BF4)为溶剂,对甲基苯磺酸根(OTs-)为阴离子的功能化离子液体[bmim]OTs为催化剂进行苯甲醇的乙酰化反应.结果表明,该体系循环使用10次后仍能保持良好的催化活性和稳定性,并对各种(伯、仲、叔)醇类、酚类和胺类化合物的乙酰化反应表现出良好的普适性.核磁共振波谱(13C NMR)分析结果表明,具有亲核性的[bmim]OTs和酰化试剂乙酸酐(Ac2O)形成的活性中间体AcOTs,是催化反应的活性物种.     

Catalytic C(1), C(2)-Bond Cleavage of Long-Chain Aliphatic Alcohols and ω-Phenylalkyl Alcohols

A catalytic one step procedure for the C(1), C(2)-bond cleavage of long-chain aliphatic alcohols and ω-phenyl alcohols has been investigated, using as examples decanol, dodecanol, hexadecanol, benzyl alcohol, 2-phenylethanol and 3-phenyl-propanol. The reactions, which were carried out in a continuous flow tubular reactor using a Ni/Cu catalyst, showed good activity and selectivity with respect to the cleavage products. On the basis of the experimental studies a reaction scheme for the heterogeneous catalytic C(1), C(2)-bond cleavage of the alcohols is suggested.     

Comparison of TEMPO and its derivatives as mediators in laccase catalysed oxidation of alcohols

A series of TEMPO (2,2′,6,6′-tetramethylpiperidinyl-1-oxy) derivatives were studied as mediators of laccase (from Trametes versicolor) in the oxidation of benzyl alcohol and 1-phenylethyl alcohol. TEMPO (1), 4-hydroxy-TEMPO (2) and 4-acetylamino-TEMPO (4) turned out to be the most active mediators for laccase. In addition, 4-acetylamino-TEMPO and 4-hydroxy-TEMPO were more active in the oxidation of 1-phenylethanol compared to TEMPO. For these mediators kinetic isotope effects in the range of 2.1-3.2 were observed for α-monodeutero-p-methylbenzyl alcohol oxidation. These values are consistent with a mechanism involving oxoammonium intermediacy. Competition experiments between benzyl alcohol and 1-phenylethanol showed that TEMPO and its derivatives react faster with primary alcohols than with secondary alcohols, also in line with the proposed mechanism.     

A model reaction assesses contribution of h-tunneling and coupled motions to enzyme catalysis

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.     

A catalytic one-step process for the chemo- and regioselective acylation of monosaccharides

An organocatalytic method for the chemo- and regioselective acylation of monosaccharides has been developed. Treatment of octyl beta-D-glucopyranoside with isobutyric anhydride in the presence of 10 mol % of a C2-symmetric chiral 4-pyrrolidinopyridine catalyst (1) at -50 degrees C gave the 4-O-isobutyryl derivative as the sole product in 98% yield. Thus, chemoselective acylation, favoring a secondary hydroxyl group in the presence of a free primary hydroxyl group, and regioselective acylation, favoring one of three secondary hydroxyl groups, took place with perfect selectivity. A competitive acylation between octyl beta-D-glucopyranoside and a primary alcohol (2-phenylethanol) with 1.1 equiv of isobutyric anhydride in the presence of 1 gave the 4-O-isobutyrate of octyl beta-D-glucopyranoside with 99% regioselectivity in 98% yield, which indicates that acylation of the secondary hydroxyl group at C(4) of the carbohydrate proceeds in an accelerative manner. A possible mechanism, involving multiple hydrogen-bonding between 1 and the monosaccharide, is proposed for the chemo- and regioselective acylation.     

Reaction of essentially free benzyl cations with acetonitrile; synthesis of ethanimidic carboxylic anhydrides and unsymmetrical diacylamines

Benzyl cations were generated via the thermal decomposition of N-benzyl-N-nitrosopivalamide in acetonitrile and acetonitrile-water mixtures at 25 degrees C. The first-formed (primary) benzylating agent, the benzyl cation, was scavenged competitively by pivalate (trimethyl acetate) ion to yield benzyl pivalate, by acetonitrile to yield the corresponding N-benzylnitrilium ion, and by water (when present) to yield benzyl alcohol. The nitrilium ion underwent a cascade of reactions to yield an array of products whose identities and relative yields as a function of time were used to elucidate the mechanistic paths involved. Thus, the N-benzylnitrilium ion reacted with pivalate ion to yield the Z-isomer of N-benzylethanimidic pivalic anhydride, followed by its conversion into the E-isomer. This article appears to be the first to document compounds of this type. The E-isomer is labile under the reaction conditions, rearranging into N-acetyl-N-pivalylbenzylamine. In the presence of water as a diluent, a significant fraction of the nitrosoamide was hydrolyzed to benzyl alcohol; hydrolysis of the nitrilium ion yielded N-benzyl acetamide. The yield of hydrosylates was directly proportional to the mole fraction of water in the medium.     

Bimetallic Au/Pd catalyzed aerobic oxidation of alcohols in the poly(ethylene glycol)/CO2 system

Bimetallic Au/Pd nanoparticles were prepared and used to catalyze oxidation of alcohols in the poly(ethylene glycol) (PEG)/CO₂ biphasic system using O₂ as the oxidant without adding any base. The catalytic activity of Au/Pd bimetal with different mole ratios was studied using benzyl alcohol as the substrate. It was found that bimetallic Au/Pd nanoparticles with Au:Pd=1:3.5 had higher catalytic activity than monometallic Au, Pd and the bimetallic Au/Pd nanoparticles with other molar ratios. The effect of CO₂ pressure on the oxidation of benzyl alcohol and 1-phenylethanol in PEG/CO₂ was investigated. It was demonstrated that CO₂ pressure could be used to tune the conversion and selectivity of the reactions effectively. α,β,-Unsaturated alcohols were also studied and found to be more reactive than benzyl alcohol and 1-phenylethanol. Recycling experiments showed that the Au/Pd/PEG/CO₂ catalytic system could be recycled at least four times without reducing the activity. In addition, the catalytic system is clean and the products can be separated easily.     

分子筛催化苯甲醛与醇缩合反应的研究

1　引言分子筛作为催化剂由于其特殊的酸性和择形性在精细有机合成中获得了广泛的应用[1],在缩醛化反应中也表现出了良好的催化性能,如Joshi[2]等用HY和HZSM5分子筛作催化剂,将苯甲醛与甲醇缩合,获得了83%的苯甲缩甲醛,并考察了不同种类的醛在HZSM5分子筛上的择形性。王存...     

Gas-chromatographic determination of formic acid in the oxidation products of organic substances

Procedures for the gas-chromatographic determination of formic acid in oxidation produts of organic substances after its conversion to benzyl formate were developed. In determining formic acid in an organic phase, free formic acid was esterified with benzyl alcohol in a pyridine solution while adding acetic anhydride under mild conditions. The conversion of formic acid was complete even in the presence of other mono-and dicarboxylic acids in considerable amounts. It was found that the formation of benzyl formate occurred via a mixed aldehyde formed in situ from formic acid and acetic anhydride. The determination of formic acid in aqueous solutions involves the synthesis of its sodium or potassium salt and the successive treatment of this salt with acetyl chloride and benzyl alcohol in a pyridine solution.