Chemoselective Protection of Hydroxyl Groups and Deprotection of Silyl Ethers

 Trimethylsilylation of alcohols and phenols is carried out using hexamethyldisilazane and LiClO₄ under microwave irradiation and neutral conditions. The deprotection of silyl ethers is carried out similarly using natural kaolinitic clay and a few drops of water.     

Vanadium Hydrogen Sulfate (I): Chemoselective Trimethylsilylation of Alcohols and Deprotection of Trimethylsilyl Ethers

Trimethylsilylation of alcohols with hexamethyldisilazane (HMDS) catalyzed by V(HSO₄)₃ under mild and completely heterogeneous reaction condition is reported. The method is highly chemoselective for the protection of alcohols in the presence of phenols, amines and thiols. Also, the deprotection of trimethylsilyl ethers is performed in the presence of V(HSO₄)₃ at room temperature in good to high yields.     

Chemoselective Preparation of Oximes, Semicarbazones, and Tosylhydrazoneswithout Catalyst and Solvent

Summary.  A simple and versatile method for the synthesis of oximes, semicarbazones, and tosylhydrazones of aldehydes in the presence of ketones without catalyst and solvent is presented. Received June 28, 2000. Accepted (revised) August 25, 2000     

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.     

Zinc Mediated Reactions in Organic Synthesis: Efficient Synthesis of Silyl Ethers under Mild Conditions

General and practical method for the synthesis of silyl ethers in the presence of zinc powder under mild conditions has been described.     

Ammonium Chlorochromate Adsorbed on Montmorillonite K-10: Oxidative Deprotection of Tetrahydropyranyl Ethers Using Microwaves in a Solventless System

Summary.  Tetrahydropyranyl ethers were rapidly and selectively oxidized to the corresponding carbonyl compounds by clay supported ammonium chlorochromate under solvent free conditions using microwaves. Received July 25, 2000. Accepted September 7, 2000     

Efficient and Selective Conversion of Trimethylsilyl and Tetrahydropyranyl Ethers to their Corresponding Acetates and Benzoates Catalyzed by Bismuth(III) Salts

Summary.  A variety of TMS and THP ethers are efficiently converted to their corresponding acetates and benzoates with acetic and benzoic anhydrides in the presence of catalytic amounts of Bi(III) salts such as BiCl₃, Bi(TFA)₃, and Bi(OTf)₃. The present method is also effective for the selective acetylation and benzoylation of TMS and THP ethers of alcohols in the presence of phenolic ethers. Received May 21, 2001. Accepted June 25, 2001     

Microwave Assisted Deprotection of N,N-Dimethylhydrazones in Water Using Palladium Chloride–Tin Chloride as Catalyst

Summary.  N,N-Dimethylhydrazones of ketones and aldehydes undergo facile cleavage to the corresponding carbonyl compounds upon exposure to microwaves in water containing a catalytic amount of PdCl₂–SnCl₂ in high yields. Corresponding authors. E-mail: rahman@umz.ac.ir Received December 27, 2001. Accepted (revised) February 6, 2002     

Palladium-catalyzed protection of alcohols and cleavage of triethylsilyl ethers

The versatility of the palladium (II) chloride/organosilane system has been tested in the transformation of alcohols to the corresponding silyl ethers and the subsequent deprotection of triethylsilyl ethers to the parent alcohols. The reaction takes place under mild conditions and affords high yields.     

Oxidative Deprotection Of Trimethylsilyl and Tetrahydropyranyl Ethers and Ethylene Acetals With Benzyltriphenylphosphonium Peroxomonosulfate in the Presence of Bismuth Chloride Under Non-Aqueous Conditions

Abstract

Benzyltriphenylphosphonium peroxomonosulfate (BnPh₃P⁺HSO₅ ^?) (1) is used as a new reagent for oxidative deprotection of trimethylsilyl and tetrahydropyranyl ethers and ethylene acetals to afford carbonyl compounds in refluxing acetonitrile in the presence of bismuth chloride.     

Lipases as Useful Tools for the Stereo- and Regioselective Protection and Deprotection of Carbohydrates

Summary.  Stereo- and regioselective acylation and deacylation of carbohydrates can be achieved using lipases as biocatalysts. These enzymes are extremely versatile, quite stable in aqueous and organic solvents, easily available, and easy to handle. Recently, they have become the object of site directed mutagenesis which suggests that they soon could be ‘built ad hoc’ for specific necessities. Received September 11, 2001. Accepted November 19, 2001     

Simple and Efficient Method for the Protection of Hydroxyl Groups as 4-Methoxybenzyl Ethers

PMB ethers of alcohols are obtained in good yields and under mild conditions using the 4-methoxybenzyl N-allyl thiocarbamate and N-bromosuccinimide (NBS)/TfOH as the catalyst. The present method is very fast, simple, and efficient.     

Synthesis and Structure of O-silylated 2-Polyfluoroacyl-cycloalkanones

Summary.  2-Acyl-cycloalkanones containing polyfluoroalkyl groups react with dichlorodimethylsilane to form the corresponding heterocyclic bis-enol derivatives. The reaction of 2-polyfluoroacyl-cycloalkanones with chlorotrimethylsilane leads to mixtures of the corresponding (Z)-configured O-silylethers. The silatropy process in this case is slow on the NMR time scale. Received February 26, 2001. Accepted (revised) March 27, 2001     

Catalytic Acetylation of Alcohols and Phenols with Potassium Dodecatungstocobaltate Trihydrate

Summary.  Alcohols and phenols are converted to esters in a mild, clean, and efficient reaction with acetic anhydride in the presence of a catalytic amount of potassium dodecatungstocobaltate trihydrate (K₅CoW₁₂O₄₀ · 3H₂O). Received August 27, 2001. Accepted (revised) October 29, 2001     

Zeofen: A User-Friendly Catalyst for Oxidative Cleavage of Tetrahydropyranyl Ethers Under Non-Aqueous Conditions

Summary.  Primary and secondary tetrahydropyranyl ethers are efficiently converted to carbonyl compounds in excellent yields by zeofen under non-aqueous conditions. Received November 21, 2000. Accepted (revised) January 9, 2001     

醇(酚)羟基的硅烷化保护与去保护研究进展

醇(酚)羟基的硅烷化保护是一类重要的有机合成手段,目的在于使羟基稳定化,消除或减轻其引起的副反应。保护基中硅原子连接的基团空间位阻越小,该保护基的反应活性越大,生成的相应硅醚的稳定性则越差,在弱酸或弱碱的条件下即可脱除;硅原子连接的基团越大,该保护基的反应活性则越小,硅醚化反应越难发生,需要借助催化剂才能进行。本文尽可能全面地论述了有机硅烷保护基的类型,如三甲基硅烷、三乙基硅烷、叔丁基二甲基硅烷、三异丙基硅烷、苯基取代硅烷和桥型硅烷等,并讨论了其在不同环境下的活性及稳定性。     

Silylation of Hydroxy Groups with HMDS Under Microwave Irradiation and Solvent-Free Conditions

Phenols and alcohols are silylated with hexamethyldisilazane (HMDS) under microwave irradiation in solvent-free condition in good to excellent yields.     

Synthesis of functionalized 4-chlorophenols and 1,4-dihydroquinones by [3+3] cyclization of 1,3-bis-silyl enol ethers with 2-chloro- and 2-acyloxy-3-(silyloxy)alk-2-en-1-ones

Functionalized 4-chlorophenols and 1,4-dihydroquinones were prepared by [3+3] cyclization of 1,3-bis-silyl enol ethers with 2-chloro- and 2-acyloxy-3-(silyloxy)alk-2-en-1-ones.