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.     

Electron-deficient [Ti(salophen)(OTf)2]: A new and highly efficient catalyst for the acetylation of alcohols and phenols with acetic anhydride

In the present work, a highly efficient method for acetylation of alcohols and phenols with acetic anhydride catalyzed by high-valent [Ti^IV(salophen)(OTf)₂] is reported. Under these conditions, primary, secondary and tertiary alcohols as well as phenols were acetylated with short reaction times and high yields. The catalyst was reused several times without loss of its catalytic activity.     

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.     

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.     

[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.     

Highly efficient tetrahydropyranylation of alcohols and phenols catalyzed by a new and reusable high-valent vanadium(IV) porphyrin

In the present work, the catalytic activity of high-valent tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂], in the tetrahydropyranylation of alcohols and phenols with 3,4-dihydro-2H-pyran (DHP) is reported. This new electron-deficient V(IV) compound was used as a highly efficient catalyst for pyranylation of primary (aliphatic and benzylic), sterically-hindered secondary and tertiary alcohols with DHP. Tetrahydropyranylation of phenols with DHP was also performed to afford the desired THP-ethers. The chemoselectivity of this method was also investigated. The results indicated that primary alcohols are more reactive in the presence of secondary and tertiary alcohols and phenols. This catalyst was reused several times without loss of its activity.     

Electron‐deficient vanadium(IV) tetraphenylporphyrin: A new,highly efficient and reusable catalyst for chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane

In the present work, the application of electron‐deficient tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V^IV(TPP)(OTf)₂], in the trimethylsilylation of alcohols and phenols with hexamethydisilazane (HMDS) is reported. This new V(IV) catalyst was used as an efficient catalyst for silylation of not only primary alcohols but also sterically hindered secondary and tertiary alcohols with HMDS. Trimethylsilylation of phenols with HMDS was also performed to afford the desired Trimethylsilyl ethers (TMS) ethers. The chemoselectivity of this method was also investigated. This catalyst can be reused several times without loss of its activity. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

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.     

Zirconyl triflate: A new, highly efficient and reusable catalyst for acetylation and benzoylation of alcohols, phenols, amines and thiols with acetic and benzoic anhydrides

Highly efficient acetylation and benzoylation of alcohols, phenols, amines and thiols with acetic and benzoic anhydrides catalyzed by new and reusable zirconyl triflate, ZrO(OTf)₂, is reported. The high catalytic activity of electron deficient ZrO(OTf)₂ can be used for the acetylation and benzoylation of not only primary alcohols but also sterically-hindered secondary and tertiary alcohols with acetic and benzoic anhydrides. Acetylation of phenols with acetic and benzoic anhydrides was achieved to afford the desired acetates and benzoates efficiently. This catalyst also efficiently catalyzed the acetylation and benzoylation of amines and thiols whereby the corresponding amides and thioesters were obtained in good to excellent yields. This catalyst can be reused several times without loss of its activity.     

Polystyrene-supported GaCl3: A new,highly efficient and recyclable heterogeneous Lewis acid catalyst for acetylation and benzoylation of alcohols and phenols

A new, simple and highly chemoselective method for both acetylation and benzoylation of alcohols and phenols with acetic anhydride in the presence of polystyrene-supported gallium trichloride (PS/GaCl₃) as a highly active and reusable heterogeneous Lewis acid catalyst is presented. In this catalytic system, primary, secondary and tertiary alcohols as well as phenols were converted to the corresponding acetates and benzoates with high yields. The heterogenized catalyst is of high reusability and stability in the acetylation 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. Remarkably, a selective mono-acetylation of symmetrical diols can be achieved chemoselectively by employing the same catalyst.     

Trinuclear tin salicylaldoximate cluster‐catalyzed selective acylation of alcohols

The reactivity and catalytic potential of the tin salicylaldoximate cluster [(Me₂Sn)₂(Me₂SnO)(OCH₃) (HONZO)(ONZO)] ( 1 ), with HONZOH = o‐HON?CH? C₆H₄OH, on the acylation reaction of various alcohols with ethyl acetate is reported. The catalyst is active toward primary and unhindered secondary alcohols, but inefficient toward tertiary and secondary bulky alcohols and phenols. A possible mechanism for the transesterification reaction catalyzed by 1 , accounting for the influence of steric factors, is proposed. Copyright © 2005 John Wiley & Sons, Ltd.     

Highly efficient protection of alcohols and phenols catalysed by tin porphyrin supported on MIL‐101

The catalytic activity of 5,10,15,20‐tetrakis(4‐aminophenyl)porphyrinatotin(IV) trifluoromethanesulfonate, [Sn^IV(TNH₂PP)(OTf)₂], supported on chloromethylated MIL‐101, was investigated in the trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) and also their tetrahydropyranylation with 3,4‐dihydro‐2H‐pyran. Excellent yields, mild reaction conditions, short reaction times and reusability of the catalyst without significant decrease in its initial activity are noteworthy advantages of this supported catalyst. Copyright © 2015 John Wiley & Sons, Ltd.     

Cross‐linked poly(4‐vinylpyridine/styrene) copolymer‐supported bismuth(III) triflate: an efficient heterogeneous catalyst for silylation of alcohols and phenols with HMDS

Cross‐linked poly(4‐vinylpyridine/styrene) copolymer‐supported bismuth(III) triflate (³⁰P/S‐Bi) effectively activates hexamethyldisilazane (HMDS) for the silylation of alcohols and phenols. By the use of this heterogeneous catalytic system, a wide range of alcohols as well as phenols are converted into their corresponding trimethylsilyl ethers in high yield under mild reaction conditions. The catalyst was reused more than 10 times without significant loss of its catalytic activity. Copyright © 2011 John Wiley & Sons, Ltd.     

Alumina Perchloric Acid (Al 2 O 3 -HClO 4 ) as an Efficient Heterogeneous Catalyst for Modified Preparation of Trimethylsilyl Ethers

A highly efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, benzylic, secondary, hindered secondary, tertiary, phenols, and oximes with hexamethyldisilazane (HMDS) using alumina perchloric acid (Al ₂ O ₃ -HClO ₄ ) as recyclable heterogeneous catalyst in excellent yields with short reaction times (3?65 min) under ambient conditions is described.     

Development of a General Non‐Noble Metal Catalyst for the Benign Amination of Alcohols with Amines and Ammonia

The N‐alkylation of amines or ammonia with alcohols is a valuable route for the synthesis of N‐alkyl amines. However, as a potentially clean and economic choice for N‐alkyl amine synthesis, non‐noble metal catalysts with high activity and good selectivity are rarely reported. Normally, they are severely limited due to low activity and poor generality. Herein, a simple NiCuFeO_x catalyst was designed and prepared for the N‐alkylation of ammonia or amines with alcohol or primary amines. N‐alkyl amines with various structures were successfully synthesized in moderate to excellent yields in the absence of organic ligands and bases. Typically, primary amines could be efficiently transformed into secondary amines and N‐heterocyclic compounds, and secondary amines could be N‐alkylated to synthesize tertiary amines. Note that primary and secondary amines could be produced through a one‐pot reaction of ammonia and alcohols. In addition to excellent catalytic performance, the catalyst itself possesses outstanding superiority, that is, it is air and moisture stable. Moreover, the magnetic property of this catalyst makes it easily separable from the reaction mixture and it could be recovered and reused for several runs without obvious deactivation.     

Commercial Zinc Oxide (Zn2+) as an Efficient and Environmentally Benign Catalyst for Homogeneous Benzoylation of Hydroxyl Functional Groups

The solvent‐free O‐acylation of some alcohols with benzoyl chloride was carried out to the corresponding benzoylated products in good to excellent yields by the mediation of a catalytic amount (5 mol%) of the commercially available and inexpensive zinc oxide in short reaction times. This methodology represents an eco‐friendly and simple catalytic alternative for benzoylation of primary, secondary, tertiary, and benzylic alcohols with ZnO. This catalytic system was homogeneous because of high solubility of zinc oxide in the reaction medium. Findings showed that ZnO was dissolved in hydrochloric acid, created in situ, after a few minutes. Although, others argued on the catalytic role of solid phase zinc oxide under a heterogeneous condition, it is not surprising to emphasize on the catalytic function of Zn²⁺ in the benzoylation of alcohols under homogeneous reaction conditions. Zinc oxide served as pre‐catalyst to form Zn²⁺, as the catalytically active species.     

RuIII(OTf)SalophenCH2–NHSiO2–Fe: an efficient and magnetically recoverable catalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane

Efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by ruthenium(III) complex of chloromethylated Salophen supported on nanomagnetic materials is reported. First, the iron nanomagnets were silica coated, functionalized with amine and then ruthenium CM‐Salophen was successfully bonded to their surface. The catalyst, Ru^III(OTf)SalophenCH₂–NHSiO₂–Fe, was characterized by elemental analysis, FT‐IR and UV–visible spectroscopic techniques, transmission electron microscopy and inductively coupled plasma (ICP). The Ru^III(OTf)SalophenCH₂–NHSiO₂–Fe catalyzed trimethylsilylation of primary and secondary alcohols as well as phenols, and the corresponding TMS ethers were obtained in high yields and short reaction times at room temperature. This new heterogenized trimethylsilylation catalyst is easily recovered with a magnet and showed no appreciable loss of activity even after five consecutive runs. Copyright © 2014 John Wiley & Sons, Ltd.     

The “Borrowing Hydrogen Strategy” by Supported Ruthenium Hydroxide Catalysts: Synthetic Scope of Symmetrically and Unsymmetrically Substituted Amines

The N‐alkylation of ammonia (or its surrogates, such as urea, NH₄HCO₃, and (NH₄)₂CO₃) and amines with alcohols, including primary and secondary alcohols, was efficiently promoted under anaerobic conditions by the easily prepared and inexpensive supported ruthenium hydroxide catalyst Ru(OH)_x/TiO₂. Various types of symmetrically and unsymmetrically substituted “tertiary” amines could be synthesized by the N‐alkylation of ammonia (or its surrogates) and amines with “primary” alcohols. On the other hand, the N‐alkylation of ammonia surrogates (i.e., urea and NH₄HCO₃) with “secondary” alcohols selectively produced the corresponding symmetrically substituted “secondary” amines, even in the presence of excess amounts of alcohols, which is likely due to the steric hindrance of the secondary alcohols and/or secondary amines produced. Under aerobic conditions, nitriles could be synthesized directly from alcohols and ammonia surrogates. The observed catalysis for the present N‐alkylation reactions was intrinsically heterogeneous, and the retrieved catalyst could be reused without any significant loss of catalytic performance. The present catalytic transformation would proceed through consecutive N‐alkylation reactions, in which alcohols act as alkylating reagents. On the basis of deuterium‐labeling experiments, the formation of the ruthenium dihydride species is suggested during the N‐alkylation reactions.     

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.