An Efficient and Highly Chemoselective Method to Desilylate Silyl Ethers

An efficient and highly chemoselective desilylating method is described. Trimethylsilyl ethers (0.25 M) in a CH₃OH/CCl₄ (1:1) solvent mixture are deprotected to their corresponding alcohols with ultrasound in a commercial ultrasonic cleaning bath. Selective deprotection of tert-butyldimethylsilyl ethers of benzyl alcohols and phenols is achieved under ultrasonic conditions. We deprotected also tert-butyldimethylsilyl ethers of primary alcohols, whereas tert-butyldimethylsilyl ethers of secondary and tertiary alcohols are stable under these conditions.     

A Mild,Simple, Efficient,and Selective Protection of Hydroxyl Groups Using Silica-Supported Sodium Hydrogen Sulfate as a Heterogeneous Catalyst

A mild, simple, novel, and highly efficient method for the rapid protection of various primary, secondary, tertiary aliphatic alcohols, aromatic alcohols, and oximes using hexamethyldisilazane (HMDS) in the presence of silica-supported sodium hydrogen sulfate (NaHSO ₄ -SiO ₂ ), as an active, inexpensive, nontoxic, heterogeneous, and readily available catalyst under ambient conditions is described. Timethylsilyl ethers were prepared in high to excellent yields, with short reaction times under mild and almost neutral reaction conditions at room temperature.     

A Facile and Efficient Trimethylsilylation of Hydroxyl Groups Using Silica-Supported Zinc Chloride and Alumina-Supported Sodium Hydrogensulfate as Recyclable Heterogeneous Catalysts

Silica-supported zinc chloride (SiO₂-ZnCl₂) and novel alumina-supported sodium hydrogensulfate (NaHSO₄-Al₂O₃) as recyclable heterogeneous catalysts have been used for the mild trimethylsilylation of hydroxyl groups under ambient conditions. This procedure also allows for the selective protection of primary and secondary alcohols in the presence of tertiary alcohols.     

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.     

Microwave-assisted rapid and efficient deprotection and direct esterification and silylation of MOM and EOM ethers catalyzed by [Hmim][HSO4] as a Br?nsted acidic ionic liquid

Abstract  

1-Methylimidazolium hydrogensulfate, [Hmim][HSO₄], a Br?nsted acidic room temperature ionic liquid, is used as a catalyst and reaction medium for facile and eco-friendly deprotection of methoxymethyl (MOM) and ethoxymethyl (EOM) ethers to their corresponding alcohols under thermal conditions (Δ) and microwave irradiation (MW). Furthermore, one-pot interconversion to the respective acetates and trimethylsilyl (TMS) ethers was also achieved.     

Selective tetrahydropyranylation of alcohols and phenols using titanium(IV) salophen trifluoromethanesulfonate as an efficient catalyst

Titanium(IV) salophen trifluoromethanesulfonate, [Ti^IV(salophen)(OSO₂CF₃)₂], as a catalyst enables selective tetrahydropyranylation of alcohols and phenols with 3,4‐dihydro‐2H‐pyran. Using this catalytic system, primary, secondary and tertiary alcohols, as well as phenols, were converted to their corresponding tetrahydropyranyl ethers in high yields and short reaction times at room temperature. Investigation of the chemoselectivity of this method showed discrimination between the activity of primary alcohols in the presence of secondary and tertiary alcohols and phenols. This heterogenized catalyst could be reused several times without loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Niobium(V) chloride catalyzed microwave assisted synthesis of 2,3-unsaturated O-glycosides by the Ferrier reaction

NbCl₅ catalyzes the Ferrier reaction of per-O-acetylated glycals with primary, secondary, allylic, benzylic and monosaccharide alcohols to give 2,3-unsaturated α-glycosides in short reaction times under microwave irradiation conditions.     

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.     

Microwave‐Assisted NiCl2 Promoted Acylation of Alcohols

Abstract

A microwave oven acylation of alcohols by carboxylic acid anhydrides has been developed. NiCl₂ has been proven an efficient catalyst for the acylation of primary, secondary, and tertiary alcohols and phenols under microwave conditions.     

[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.     

Preparation of Silyl Ethers Using Hexamethyldisilazane in the Presence of N‐Bromosuccinimide under Mild and Solvent‐Free Conditions

A mild, simple, novel and highly efficient method for the rapid protection of various primary, secondary, tertiary aliphatic and aromatic alcohols using hexamethyldisilazane (HMDS) in the presence of N-bromosuccinimide (NBS) as an active, inexpensive, non-toxic and readily available catalyst under solvent-free conditions is described. Trimethylsilyl ethers were prepared in high to excellent yields with short reaction time under mild and almost neutral reaction conditions.     

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.     

A novel B(C(6)F(5))(3)-catalyzed reduction of alcohols and cleavage of aryl and alkyl ethers with hydrosilanes

The primary alcohols 1a-e and ethers 4a-d were effectively reduced to the corresponding hydrocarbons 2 by HSiEt(3) in the presence of catalytic amounts of B(C(6)F(5))(3). To the best of our knowledge, this is the first example of catalytic use of Lewis acid in the reduction of alcohols and ethers with hydrosilanes. The secondary alkyl ethers 4j,k enabled cleavage and/or reduction under similar reaction conditions to produce either the silyl ethers 3m-n or the corresponding alcohol 5a upon subsequent deprotection with TBAF. It was found that the secondary alcohols 1g-i and tertiary alcohol 1j, as well as the tertiary alkyl ether 4l, did not react with HSiEt(3)/(B(C(6)F(5))(3) reducing reagent at all. The following relative reactivity order of substrates was found: primary > secondary > tertiary. A plausible mechanism for this nontraditional Lewis acid catalyzed reaction is proposed.     

A facile method for the rapid and selective deprotection of methoxymethyl (MOM) ethers

We describe a rapid and efficient method for selective deprotection of methoxymethyl (MOM) ethers using ZnBr₂ and n-PrSH, which completely removed MOM from diverse MOM ethers of primary, secondary, and tertiary alcohols or phenol derivatives. The deprotection takes less than ten minutes with both high yield and selectivity in the presence of other protecting groups. In addition, the rapid deprotection of MOM ethers of tertiary hydroxyls in high yield with no epimerization allows MOM to be a suitable protecting group for tertiary alcohols.     

三溴异氰脲酸和DABCI-Br作为高效催化剂用于羟基硅烷化

The protection and deprotection of functionalgroups are indispensable in the synthesis of polyfunc-tional compounds.In addition,several chemical con-versions and multiple sequence syntheses are often re-quired for the protection of hydroxyl groups.Thesily…     

Quinoxalinium Fluorochromate (QxFC): A New and Efficient Reagent for the Oxidation of Alcohols in Solution,Under Solvent-Free Conditions and Microwave Irradiation

The new mild oxidizing agent, quinoxalinium fluorochromate (QxFC), has been easily prepared by reacting quinoxaline with an aqueous solution of CrO ₃ and HF. This reagent is suitable for oxidizing various primary and secondary alcohols to their corresponding carbonyl compounds and anthracene to antraquinone. The reactions were carried out in solution, under solvent-free conditions and microwave irradiation. The results show that the rates of the reactions and the yields are usually highest under microwave irradiation.     

Highly effective methane conversion to aromatic hydrocarbons by means of microwave and rf-induced catalysis

Conversion of methane to higher hydrocarbon products, in particular, aromatic hydrocarbons has been achieved with good methane conversion and selectivity to aromatic products over heterogeneous catalysts using both high power pulsed microwave and rf energy. For example, under microwave irradiation > 85% conversion of methane and 60% selectivity to aromatics could be achieved. Cu, Ni, Fe and Al metallic materials are highly effective catalysts for the aromatization of methane via microwave heating; however, with a variety of supported catalysts the major products were C₂ hydrocarbons and the conversion of methane was low. The use of sponge, wire and net forms of these metal catalysts was found advantageous in effective methane conversion. The reactions are considered to be free radical in nature and to proceed through an intermediate stage involving formation of acetylene. The influence of catalyst nature and configuration, as well as the microwave and rf irradiation parameters on the reaction efficiency and product selectivity has been examined in both batch and continuous flow conditions.     

Preparation of Silica Supported Tin Chloride: As a Recyclable Catalyst for the Silylation of Hydroxyl Groups with HMDS

Silica‐supported tin chloride [SiO₂‐Sn(Cl)_4‐n] has been prepared by mixing tin chloride with activated silica gel in toluene under refluxing conditions for one day. A range of primary, secondary, and tertiary alcohols as well as phenolic hydroxyl groups were converted into their corresponding trimethylsilyl ethers with hexamethyldisilazane in the presence of catalytic amounts of silica‐supported tin chloride at room temperature. An excellent chemoselective silylation of hydroxyl groups in the presence of other functional groups was also observed. This catalyst could be recycled and reused fifteen times without loss of efficiency.     

Efficient Difluoromethylation of Alcohols Using TMSCF2Br as a Unique and Practical Difluorocarbene Reagent under Mild Conditions

A general method for the efficient difluoromethylation of alcohols using commercially available TMSCF₂Br (TMS=trimethylsilyl) as a unique and practical difluorocarbene source is developed. This method allows primary, secondary, and even tertiary alkyl difluoromethyl ethers to be synthesized under weakly basic or acidic conditions. The reaction mainly proceeds through the direct interaction between a neutral alcohol and difluorocarbene, which is different from the difluoromethylation of phenols. Moreover, alcohols containing other moieties that are also reactive toward difluorocarbene can be transformed divergently by using TMSCF₂Br. This research not only solves the synthetic problem of difluorocarbene‐mediated difluoromethylation of alcohols, it also provides new insights into the different reaction mechanisms of alcohol difluoromethylation and phenol difluoromethylation with difluorocarbene species.     

High-valent [Sn(Br8TPP)(OTf)2] as a highly efficient and reusable catalyst for selective methoxymethylation of alcohols and phenols: The effect of substituted bromines on the catalytic activity

High-valent tin(IV)octabromotetraphenylporphyrinato trifluoromethanesulfonate, [Sn^IV(Br₈TPP)(OTf)₂], was used for selective methoxymethylation of alcohols and phenols with formaldehyde dimethyl acetal (FDMA) at room temperature. Different primary, secondary and tertiary alcohols as well as phenols were converted to their corresponding methoxymethyl ethers with FMDA in the presence of an electron deficient tin(IV) porphyrin. The catalyst was reused several times without significant loss of its activity.