Unexpected deprotection of silyl and THP ethers induced by serious disparity in the quality of Pd/C catalysts and elucidation of the mechanism

Commercial Pd/C catalysts show different catalytic activity toward the deprotection of silyl and THP ethers. The Pd/C purchased from Merck and ACROS exhibits marked tendency to cleave these protective groups unexpectedly without hydrogen conditions although Aldrich's Pd/C (20,569-9) is inactive in the absence of hydrogen. It was proved that the Pd/C disparity toward the deprotection of TES and THP ethers results from residual acids and/or palladium chloride in the production process of Pd/Cs. Although a TES ether cleavage reaction in the absence of hydrogen and a THP ether cleavage reaction in the presence of hydrogen using 10% Pd/C were recently published, we could conclude they were only an acid-catalyzed solvolysis, the acid being released from the catalyst. Hydrogen is essential for the actual 10% Pd/C-catalyzed cleavage of TES ethers and THP ethers which must be stable under the true Pd/C-catalyzed hydrogenation conditions.     

A catalytic amount of nickel(II) chloride hexahydrate and 1,2-ethanedithiol is a good combination for the cleavage of tetrahydropyranyl (THP) and tert-butyldimethylsilyl (TBS) ethers

Various THP and TBS ethers can be unmasked easily to the corresponding hydroxyl compounds in good yields by using a combination of a catalytic amount of nickel(II) chloride hexahydrate and 1,2-ethanedithiol at room temperature. In addition, alkyl TBS ethers can be hydrolyzed chemoselectively in the presence of aryl TBS ethers. Moreover, alkyl TBS ethers can be cleaved easily in the presence of alkyl or aryl THP ethers using the same conditions.     

Bi(III) SALTS AS NEW CATALYSTS FOR THE SELECTIVE CONVERSION OF TRIMETHYLSILYL AND TETRAHYDROPYRANYL ETHERS TO THEIR CORRESPONDING ACETATES AND FORMATES

ABSTRACT

Bi(III) salts such as BiCl₃, Bi(TFA)₃ and Bi(OTf)₃ were found to be efficient catalysts for the transformation of trimethylsilyl (TMS) and tetrahydropyranyl (THP) ethers to their corresponding acetates and formates with acetic acid and ethyl formate. Selective acetylation and formylation of TMS and THP ethers of alcohols in the presence of phenolic TMS and THP ethers make this method a useful and practical procedure in organic synthesis.     

Simple Protocol for Synthesis and Cleavage of Tetrahydropyranyl Ethers Using FeSO4 as an Inexpensive Catalyst

Protection and deprotection of alcohols and phenols as tetrahydropyranyl ethers (THP ethers) using an hydrous FeSO₄ under microwave irradiation without solvent is carried out.     

Simple deprotection of acetal type protecting groups under neutral conditions

When acetals such as MOM ethers, MEM ethers, and THP ethers were heated in ethylene glycol or propylene glycol, solvolysis proceeded smoothly to produce alcohols in excellent yield. This reaction is a very promising method for chemoselective deprotection of acetal type protecting groups.     

Zinc triflate: A mild and efficient catalyst for deprotection of tetrahydropyranyl ethers

Treatment of tetrahydropyranyl (THP) ethers with zinc triflate in methanol provides a simple and efficient process for deprotection of these ethers and the parent alcohols are obtained in excellent yields.     

Selective removal of tetrahydropyranyl ethers in the presence of t-butyldimethylsilyl ethers

Dimethylaluminiun chloride has been found to cleave THP ethers selectively without any removal of t-butyldimethylsilyl ethers     

Cerium(IV) sulfate tetrahydrate: a catalytic and highly chemoselective deprotection of THP,MOM, and BOM ethers

Tetrahydropyranyl (THP), methoxymethyl (MOM), and benzyloxymethyl (BOM) phenyl/alkyl ethers were efficiently cleaved to the corresponding parent hydroxyl compounds in good yields using catalytic amounts of Ce(SO₄)₂·4H₂O by microwave-assisted or conventional heating in methanol solution. Intramolecular and competitive experiments demonstrated the chemoselective deprotection of THP ethers in the presence of triisopropylsilyl (TIPS) and tert-butyldiphenylsilyl (TBDPS) phenyl ethers.     

Microwave Thermolysis: A Rapid and Selective Method for the Cleavage of THP Ethers Using CrO 3 Supported onto Zeolite in Solventless System

Oxidative deprotection of tetrahydropyranyl ethers (THP ethers) using chromium trioxide supported onto zeolite under microwave irradiation in solvent free condition is described.     

Ring cleavage of THP and THF ethers using dimethylboron bromide

The reaction of dimethylboron bromide with THP and THF ethers was studied. Under conditions of kinetic control, these reactions proceed by selective cleavage of the ring carbon—oxygen bond to give acyclic α-bromo ethers. Treatment of these intermediates with a variety of nucleophiles gives ring-opened products.     

Efficient Conversion of Tetrahydropyranyl (THP) Ethers to Their Corresponding Thiocyanates With in-situ–Generated Ph3P(SCN)2

Immediate and efficient one-pot conversion of tetrahydropyranyl (THP) ethers to their corresponding thiocyanates by in-situ–generated Ph₃P(SCN)₂ is described. Primary and secondary alkyls and also benzylic THP ethers are converted to their corresponding thiocyanates in excellent yields at room temperature by this method.     

DABCO–Bromine Complex: A Novel Oxidizing Agent for Oxidative Deprotection of THP and Silyl Ethers and Semicarbazones to Corresponding Carbonyl Compounds

A tetrameric DABCO–bromine complex was synthesized, characterized, and utilized as a novel active bromine complex for the oxidative deprotection of THP and silyl ethers and semicarbazones to carbonyl compounds.     

DIRECT OXIDATIVE DEPROTECTION OF TETRAHYDROPYRANYL ETHERS USING HEXAMETHYLENETETRAMINE-BROMINE SUPPORTED ONTO SILICA GEL UNDER MICROWAVE IRRADIATION IN SOLVENTLESS SYSTEM

Primary and secondary tetrahydropyranyl ethers (THP ethers) are converted to their corresponding carbonyl compounds efficiently using hexamethylene-tetramine-bromine supported onto silica gel under microwave irradiation in solvent-free conditions.     

A mild method for the deprotection of tetrahydropyranyl (THP) ethers catalyzed by iron(III) tosylate

A mild method for the deprotection of THP ethers catalyzed by iron(III) tosylate (2.0 mol %) in CH₃OH has been developed. Iron(III) tosylate, Fe(OTs)₃·6H₂O, is a commercially available solid that is inexpensive, noncorrosive, and easy to handle. The room temperature reaction conditions make this method attractive for deprotection of a range of THP ethers.     

Caro's Acid Supported on Silica Gel. Part V: A Mild and Selective Reagent for Conversion of Trimethyl Silyl ethers to the Corresponding Hydroxy Compounds

Mild and efficient method for deprotection of silyl ethers to alcohols is described using Caro's acid supported on silica gel. Reactions are carried out in dichloromethane at room temperature and their parent hydroxy compounds obtained in good to excellent yields. Using this procedure, tetrahydropyranyl ethers (THP) remain intact during desilylation reaction.

     

Chemoselective hydrolysis of terminal isopropylidene acetals in acetonitrile using molecular iodine as a mild and efficient catalyst

A simple, mild and efficient method for deprotection of acetonides in the presence of molecular iodine is described. Acid labile protecting groups such as PMB, OMe, OBn, allyl and propargyl are compatible with the reaction conditions, while TBS, TBDPS, TMS and THP ethers were unstable under the same conditions.     

Activation of DMSO by Phosphonitrilic Chloride: An Efficient Method for Oxidation of Alcohols

A variety of alcohols have been oxidized under mild conditions by a dimethylsulfoxide (DMSO)–chlorophosphazene complex. Sensitive groups such as silyl and tetrahydropyranyl (THP) ethers are stable under this condition.     

Chemoselective allylation of aldehydes using cerium(III) chloride: simple synthesis of homoallylic alcohols

Aldehydes undergo smooth nucleophilic addition with allyltributylstannane in the presence of CeCl₃·7H₂O in acetonitrile under extremely mild reaction conditions to afford the corresponding homoallylic alcohols in excellent yields with high chemoselectivity. This method is very useful especially for the allylation of aldehydes bearing acid sensitive functionalities such as TBDMS, THP ethers, acetonides, aryl alkyl ethers and carbamates.     

Acid catalysed reactions between diols and vinyl-ethers in basic solvents towards a selective protection of polyols by 2,3-dihydro-4H-pyran

Acid catalysed synthesis of THP ethers of 1,3-butanediol takes place much more selectively and in high yields if DMSO is used as solvent, instead in CHCl₃, even with mild acid catalysts, rearranged 1,3-dioxans are obtained.     

A Mild and Practical Procedure for Tetrahydropyranylation of Alcohols and Phenols Catalysed by Anhydrous Ferrous Sulfate

Theprotectionofhydroxybyformationoftetrahydropyranyl(THP)ethersisofgreatimportanceinorganicsynhesisparticularlyduringthesynthesisofnaturalproducts.'OwingtotheremarkablestabilityofTHPethersunderavarietyofreactionconditions,suchasneutralandstronglybasicmedia,reactionsinvolvingGrignardreagents,reductionwithhydrides,oxidation,oxidativealkylationandacylation,etc.,tetrahydropyranylationisoneofthemethodsofchoicetoprotectahydroxylgroupsinamultisteporganicsynthesis.'Generallytetrahydropyranylationofa…