An improved Cu-based catalyst system for the reactions of alcohols with aryl halides

The use of 3,4,7,8-tetramethyl-1,10-phenanthroline (Me(4)Phen) as a ligand improves the Cu-catalyzed cross-coupling reactions of aryl iodides and bromides with primary and secondary aliphatic, benzylic, allylic, and propargylic alcohols. Most importantly, by employing this catalyst system, the need to use an excessive quantity of the alcohol coupling partner is alleviated. The relatively mild conditions, short reaction times, and moderately low catalyst loading allow for a wide array of functional groups to be tolerated on both the electrophilic and nucleophilic coupling partners.     

Magtrieve™: a convenient catalyst for the oxidation of alcohols

We find that Magtrieve™ (CrO₂) catalyzes the oxidation of a wide variety of alcohols with periodic acid as the terminal oxidant. Mild conditions, short reaction times, and facile aqueous work-up make this a most attractive method. Olefins are not oxidized under these conditions; thus alcohols react selectively in the presence of alkenes. Conditions have been optimized with respect to catalyst loading, solvent, and co-oxidant; and the scope of the reaction includes primary and secondary benzylic, allylic, and aliphatic alcohols.     

FeCl3催化Et2Zn与芳香醛的加成反应研究

以FeCl_3作为催化剂, 研究了Et_2Zn与芳香醛的加成反应, 考察了催化剂、溶剂、催化剂与Et_2Zn用量及温度对该反应的影响. 实验结果表明: 在60℃, 1.2当量Et_2Zn, 甲基环戊基醚为溶剂的反应条件下, 10 mol% FeCl_3可以较高效的将各种芳香醛转化为仲醇.     

Practical Cu(OAc)2/TEMPO-catalyzed selective aerobic alcohol oxidation under ambient conditions in aqueous acetonitrile

We reported a ligand- and additive-free Cu(OAc)₂/TEMPO catalyst system that enables efficient and selective aerobic oxidation of a broad range of primary and secondary benzylic alcohols, primary and secondary 1-heteroaryl alcohols, cinnamyl alcohols, and aliphatic alcohols to the corresponding aldehydes and ketones. This ambient temperature oxidation protocol is of practical features like aqueous acetonitrile as solvent, ambient air as the terminal oxidant, and low catalyst loading, presenting a potential value in terms of both economical and environmental considerations. Based on the experimental observations, a plausible reaction mechanism was proposed.     

Sustainable synthesis of quinolines (pyridines) catalyzed by a cheap metal Mn(I)-NN complex catalyst

This study represents the first example of a bidentate phosphine-free manganese(I)-NN complex catalyst for the synthesis of quinolines (pyridines) through acceptorless dehydrogenative condensation of various secondary alcohols with amino alcohols. The coupling reactions occurred at 3 mol% catalyst loading and 110°C, and tolerated diverse functional groups. Moderate to excellent yields ranging from 45% to 89% were achieved after 12 hr of reaction. The present protocol provides a concise and environmentally friendly method for the construction of heterocyclic compounds.     

Alumina Sulfuric Acid as an Efficient and Recyclable Heterogeneous Catalyst for the O-Silylation of Alcohols,Phenols, and Oximes

Alumina sulfuric acid as a recyclable catalyst conducts the transformation of various types of alcohol, phenols, and oximes with hexamethyldisilazane (HMDS) to the corresponding O-trimethylsilylated compounds in good to excellent yields under mild and ambient conditions with short reaction times. The method is highly selective for the conversion of primary alcohols in the presence of secondary and tertiary alcohols. Additionally, the catalyst can be easily recovered and reused at least eight times without detectable loss of reactivity.     

Polystyrene‐Gallium Trichloride Complex: A Mild,Highly Efficient,and Recyclable Polymeric Lewis Acid Catalyst for Chemoselective Silylation of Alcohols and Phenols with Hexamethyldisilazane

Polystyrene‐supported gallium trichloride (PS/GaCl₃) as a highly active and reusable heterogeneous Lewis acid effectively activates hexamethyldisilazane (HMDS) for the efficient silylation of alcohols and phenols at room temperature. In this heterogeneous catalytic system, primary, secondary, and tertiary alcohols as well as phenols were converted to their corresponding trimethylsilyl ethers with short reaction times and high yields under mild reaction conditions. The heterogenized catalyst is of high reusability and stability in the silylation reactions and was recovered several times with negligible loss in its activity or a negligible catalyst leaching, and also there is no need for regeneration. It is noteworthy that this method can be used for chemoselective silylation of different alcohols and phenols with high yields.     

Highly efficient and chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by reusable electron-deficient [Ti(salophen)(OTf)2]

In the present work, highly efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by high-valent [Ti^IV(salophen)(OTf)₂] is reported. Under these conditions, primary, secondary and tertiary alcohols as well as phenols were silylated in short reaction times and high yields. It is noteworthy that this method can be used for chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity.     

[Sn(TPP)(BF4)2]: An efficient and reusable catalyst for chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane

Tin(IV)tetraphenylporphyrinato tetrafluoroborate, [Sn^IV(TPP)(BF₄)₂], was used as an efficient catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS). High-valent [Sn^IV(TPP)(BF₄)₂] catalyzes trimethylsilylation of primary, secondary and tertiary alcohols as well as phenols, and the corresponding TMS-ethers were obtained in high yields and short reaction times at room temperature. While, under the same reaction conditions [Sn^IV(TPP)Cl₂] is less efficient to catalyze these reactions. One important feature of this catalyst is its ability in the chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity.     

Efficient transesterification/acylation reactions mediated by N-heterocyclic carbene catalysts

Imidazol-2-ylidenes, a family of N-heterocyclic carbenes (NHC), are efficient catalysts in the transesterification involving numerous esters and alcohols. Low catalyst loadings of aryl- or alkyl-substituted NHC catalysts mediate the acylation of alcohols with enol acetates in short reaction times at room temperature. Commercially available and more difficult to cleave methyl esters react with primary alcohols in the presence of alkyl-substituted NHC to efficiently form the corresponding esters. While primary alcohols are selectively acylated over secondary alcohols with use of enol esters as acylating agents, methyl and ethyl esters can be employed as protective agents for secondary alcohols in the presence of the more active alkyl-substituted NHC catalysts. The NHC-catalyzed transesterification protocol was simplified by generating the imidazol-2-ylidene catalysts in situ.     

Bifunctional RuII‐Complex‐Catalysed Tandem C−C Bond Formation: Efficient and Atom Economical Strategy for the Utilisation of Alcohols as Alkylating Agents

Catalytic activities of a series of functional bipyridine‐based Ru^II complexes in β‐alkylation of secondary alcohols using primary alcohols were investigated. Bifunctional Ru^II complex ( 3 a ) bearing 6,6’‐dihydroxy‐2,2’‐bipyridine (6DHBP) ligand exhibited the highest catalytic activity for this reaction. Using significantly lower catalyst loading (0.1 mol %) dehydrogenative carbon?carbon bond formation between numerous aromatic, aliphatic and heteroatom substituted alcohols were achieved with high selectivity. Notably, for the synthesis of β‐alkylated secondary alcohols this protocol is a rare one‐pot strategy using a metal–ligand cooperative Ru^II system. Remarkably, complex 3 a demonstrated the highest reactivity compared to all the reported transition metal complexes in this reaction.     

纳米SiO2负载Preyssler杂多酸催化剂对水杨酸与苄醇或脂肪醇酯化反应的催化性能

An efficient and environmentally benign procedure for the catalytic esterification of salicylic acid with aliphatic alcohols, CnH2n+1OH(n=1-5)and benzylic alcohols,RC6H4CH2OH(R=H,NO2,OCH3,Br,Cl,Me)was developed using nano-SiO2-supported Preyssler heteropolyacid both under thermal conditions and microwave irradiation.Silica nanostructures were obtained through a sol-gel method and were characterized by transmission electron microscopy and powder X-ray diffraction.The effects of various parameters such as solvent type,molar ratio of substrates,Preyssler heteropolyacid loading on silica,catalyst amount,temperature,and reaction time were studied and the optimum conditions were obtained.It has been found that the catalyst with 30 wt%loading is highly active and shows high yields in esterification reactions.The use of nano-SiO2-supported Preyssler heteropolyacid coupled with microwave irradiation allows a solvent-free,rapid(3 min),and high-yielding reaction.This catalyst can be easily recovered and reused for many times without a significant loss in its activity.     

Efficient nickel-mediated intramolecular amination of aryl chlorides

The use of an in situ generated Ni(0) catalyst associated with 2,2'-bipyridine or N,N'-bis(2,6-diisopropylphenyl)dihydroimidazol-2-ylidene (SIPr) as a ligand and NaO-t-Bu as the base for the intramolecular coupling of aryl chlorides with amines is described. The procedure has been applied to the formation of five-, six-, and seven-membered rings. [reaction: see text]     

原子级分散Fe-N-C温和条件下选择性氧化催化特性

采用非溶液法制备了原子级分散的Fe-N-C催化剂,并用于硫醚和二级醇的选择性氧化.研究结果表明,这种原子级分散的Fe-N-C催化剂可在温和条件下选择性地将硫醚转化为亚砜,而不会产生过度氧化的砜.该工艺具有反应条件温和、反应速度快、收率高等优点;该催化剂对二级醇氧化制酮反应具有较高的催化活性,产率较高.作为一种非均相催化剂,Fe-N-C催化剂循环使用5次后活性未见显著下降;在实验结果和参考文献的基础上还提出了一种可能的自由基反应机理.     

Transesterification/Acylation of secondary alcohols mediated by N-heterocyclic carbene catalysts

N-Heterocyclic carbenes (NHC) are efficient catalysts for transesterification/acylation reactions involving secondary alcohols. The catalytic transformations are carried out employing low catalyst loadings in convenient reaction times at room temperature.     

Graphene oxide‐bound electron‐deficient tin(IV) porphyrin: a highly efficient and selective catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane

The catalytic activity of graphene oxide‐bound tetrakis(p ‐aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate, [Sn^IV(TNH₂PP)(OTf)₂], in the trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) is reported. The prepared catalyst was characterized using inductively coupled plasma analysis, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared and diffuse reflectance UV–visible spectroscopies. This heterogeneous catalyst was used for selective trimethylsilylation of various alcohols and phenols with HMDS in short reaction times and high yields. Also, the catalyst is of high reusability and stability, in that it was recovered several times without loss of its initial activity. The chemoselectivity of this catalytic system in the silylation of primary alcohols in the presence of secondary and tertiary alcohols and also phenols was investigated.     

Rice husk: Introduction of a green,cheap and reusable catalyst for the protection of alcohols,phenols, amines and thiols

A mild, efficient and eco-friendly protocol for the chemoselective protection of benzylic and primary and less hindered secondary aliphatic alcohols and phenols as trimethylsilyl ethers and different types of amines as N-tert-butylcarbamates is developed using rice husk (RiH) as the catalyst. This reagent is also able to catalyze the acetylation of alcohols, phenols, thiols and amines with acetic anhydride. Easy work-up, relatively short reaction times, excellent yields and low cost, availability and reusability of the catalyst are the striking features of this methodology, which can be considered to be one of the best and general methods for the protection of alcohols, phenols, thiols and amines. In addition, the use of a green reagent in the above-mentioned reactions results in a reduction of environmental pollution and of the cost of the applied methods.     

Synthesis of a polymer–ruthenium complex Ru(pbbp)(pydic) and its catalysis in the oxidation of secondary alcohols with TBHP as oxidant

A polymer–ruthenium complex Ru(pbbp)(pydic) was synthesized from the reaction of poly-2,6-bis(benzimidazolyl)pyridine (pbbp) with RuCl₃ and disodium pyridine-2,6-dicarboxylate (pydic). The Ru(pbbp)(pydic) was characterized thoroughly by spectroscopic methods. ICP analysis revealed that the percentage of complexation of 2,6-bis(benzimidazolyl)pyridine unit in pbbp was about 83%. The complex was tested as a heterogeneous catalyst for the oxidation of secondary alcohols to their corresponding carbonyl compounds in solvent-free conditions using aqueous tert-butyl hydroperoxide as oxidant. The developed catalytic system exhibited high activity and broad functional group compatibility, allowing a variety of secondary alcohols, including substituted secondary benzylic alcohols and secondary aliphatic ones, to be oxidized to the corresponding ketones in high yields. This Ru(pbbp)(pydic) could be recycled for several times, but it dissolved in part in the reaction mixture during the catalytic run leading to gradual deactivation of the catalyst with repeated runs.     

CuI/2,2'-联吡啶/2,2,6,6-四甲基哌啶氧化物催化氧化醇生成腈的工艺

以高压反应釜为反应装置,采用CuI/Bipy(2,2'-联吡啶)/TEMPO(2,2,6,6-四甲基哌啶氧化物)催化体系,以氨水作氮源,分子氧作氧化剂,对醇催化氧化生成相应腈的方法进行了优化。 以苯甲醇的催化氧化反应为模型反应,考察了催化剂及其用量、溶剂、反应温度以及时间对催化性能的影响。 实验表明:在高压釜中,120 ℃、40×10⁵ Pa的氮氧混合气(φ(O₂)=8%)条件下,将催化剂摩尔分数降低至1%(脂肪醇催化剂摩尔分数为5%),反应时间缩短至8 h时,催化效果最佳。同时,该反应系统对于不同的芳香醇和脂肪醇的氧化均取得了90%以上的转化率和90%以上的产品收率。     

Rapid,highly efficient and chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by reusable electron‐deficient tin(IV)porphyrin

In this paper, rapid and highly efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) in the presence of catalytic amounts of high‐valent [Sn^IV(TPP)(OTf)₂] is reported. This catalytic system catalyzes trimethylsilylation of primary, secondary and tertiary alcohols as well as phenols, and the corresponding TMS‐ethers were obtained in high yields and short reaction times at room temperature. It is noteworthy that this method can be used for chemoselective silylation of primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without loss of its catalytic activity. Copyright © 2009 John Wiley & Sons, Ltd.