Tetrabutylammonium tribromide (TBATB) as an efficient generator of HBr for an efficient chemoselective reagent for acetalization of carbonyl compounds

Acyclic and cyclic acetals of various carbonyl compounds were obtained in excellent yields under a mild reaction condition in the presence of trialkyl orthoformate and a catalytic amount of tetrabutylammonium tribromide (TBATB) in absolute alcohol. Chemoselective acetalization of an aldehyde in the presence of ketone, unsymmetrical acetal formation, shorter reaction times, mild reaction conditions, the stability of acid-sensitive protecting groups, high efficiencies, facile isolation of the desired products, and the catalytic nature of the reagent make the present methodology a practical alternative.     

An efficient and chemoselective deprotection of tert-butyldimethylsilyl (TBDMS) ethers using tailor-made ionic liquid

Phenolic tert-butyldimethylsilyl (TBDMS) ethers can be deprotected to yield phenols in excellent yield using tailor-made ionic liquid [dihexaEGim][OMs] (dihexaEGim = dihexaethylene glycolic imidazolium salt) as an organic catalyst with alkali-metal fluoride in tert-amyl alcohol. On the contrary, all TBDMS protecting groups can be cleaved cleanly from the bis-TBDMS ether using the same reaction in CH₃CN solvent instead of tert-alcohol at 100 °C. This [dihexaEGim][OMs]/tert-amyl alcohol media system allows the highly selective phenolic deprotection reaction of various bis-TBDMS ethers containing both phenolic and aliphatic TBDMS ethers to provide the corresponding phenols in high yield.     

Tetrabutylammonium tribromide as efficient catalyst in the synthesis of bis(indolyl)methanes

An efficient procedure has been developed for the synthesis of bis(indolyl)methane derivatives by condensation of aldehydes with indole in the presence of tetrabutylammonium tribromide as catalyst.     

Facile cleavage of triethylsilyl (TES) ethers using o-iodoxybenzoic acid (IBX) without affecting tert-butyldimethylsilyl (TBS) ethers

[reaction: see text] In DMSO cleavage of triethylsilyl (TES) ethers by o-iodoxybenzoic acid (IBX) was significantly faster than cleavage of tert-butyldimethylsilyl (TBS) ethers or further oxidation into carbonyl compounds. In most cases, TES protecting groups could be removed in good to excellent yields within 1 h, whereas similar TBS protecting groups remained intact under the same conditions. The procedure also could be adapted for direct one-pot conversion of TES ethers into carbonyl compounds.     

P(MeNCH2CH2)3N: an efficient catalyst for the desilylation of tert-butyldimethylsilyl ethers

tert-Butyldimethylsilyl (TBDMS) ethers of primary, secondary, and tertiary alcohols and phenolic TBDMS ethers are desilylated to their corresponding alcohols and phenols, respectively, in DMSO, at 80 degrees C, in 68-94% yield in the presence of 0.2-0.4 equiv of P(MeNCH2CH2)3N. Using P(i-PrNCH2-CH2)3N as the catalyst, 85-97% yields of desilylated alcohols were obtained from TBDMS ethers of 1-octanol, 2-phenoxyethanol, and racemic alpha-phenyl ethanol. These are the first examples of desilylations of silyl ethers catalyzed by nonionic bases. Both catalysts were much less effective for the desilylation of tert-butyldiphenylsilyl (TBDPS) ethers (22-45% yield) under the same conditions as used for TBDMS ethers. Possible pathways involving nucleophilic attack of the anion of the solvent molecule (generated by the catalyst) at the Si-O bond of silyl ether or a prior activation of the silyl ether by the catalyst via a P-Si interaction followed by nucleophilic attack of the solvent anion are proposed on the basis of 1H and 31P NMR experimental data.     

A mild and chemoselective method for the deprotection of tert-butyldimethylsilyl (TBDMS) ethers using iron(III) tosylate as a catalyst

The most common method for the deprotection of TBDMS ethers utilizes stoichiometric amounts of tetrabutylammonium fluoride, n-Bu₄N⁺F⁻ (TBAF), which is highly corrosive and toxic. We have developed a mild and chemoselective method for the deprotection of TBDMS, TES, and TIPS ethers using iron(III) tosylate as a catalyst. Phenolic TBDMS ethers, TBDPS ethers and the BOC group are not affected under these conditions. Iron(III) tosylate is an inexpensive, commercially available, and non-corrosive reagent.     

Chemoselective thioacetalisation and transthioacetalisation of carbonyl compounds catalysed by tetrabutylammonium tribromide (TBATB)

Thioacetals and thioketals of various aldehydes and ketones were obtained directly from carbonyl compounds or by a transthioacetalisation process from cyclic O,O-acetals in the presence of dithiols and a catalytic amount of tetrabutylammonium tribromide (TBATB). Chemoselective thioacetalisation of aromatic aldehydes containing an electron-donating group in the presence of an aldehyde containing an electron-withdrawing group, aldehydes in the presence of ketones, aliphatic cyclic ketones in the presence of aromatic ketones and less hindered ketones in the presence of more hindered ketones have been achieved. A cyclic acetal containing an electron-donating group has been chemoselectively transthioacetalised in the presence of an acetal having an electron-withdrawing substituent. These selectivities are due to the intrinsic reactivity of the substrate themselves and are independent of the catalyst and reaction conditions. Shorter reaction times, mild reaction conditions, stability of acid sensitive protecting groups, high efficiencies, facile isolation of the desired products and the catalytic nature of the reagent are the attractive features of the present method.     

Synthesis of highly functionalized piperidines by one-pot multicomponent reaction using tetrabutylammonium tribromide (TBATB)

Tetrabutylammonium tribromide (TBATB) has been found to be an efficient catalyst for the one-pot synthesis of highly substituted piperidines through a combination of 1,3-dicarbonyl compounds, aromatic aldehydes, and various amines in ethanol at room temperature. Atom economy, good yields, environmentally benign, and mild reaction conditions are some of the important features of this protocol.     

Polysulfones: solid organic catalysts for the chemoselective cleavage of methyl-substituted allyl ethers under neutral conditions

The solid polysulfone made of SO2 and methylidenecyclopentane catalyzes the cleavage of methyl-substituted allyl ethers and liberates the corresponding alcohols.     

Tetrabutylammonium tetra (tert-butyl alcohol) coordinated fluoride-an efficient reagent for the synthesis of fluorine derivatives of phosphorus(V) compounds

Direct conversion of phosphorus(V) chlorides to the corresponding phosphorus(V) fluorides was achieved using a solid reagent, tetrabutylammonium tetra (tert-butyl alcohol) coordinated fluoride. The phosphorus(V) fluorides were directly synthesized and efficiently isolated in very good yields.     

Zirconium(IV) chloride catalyzed new and efficient protocol for the selective cleavage of p-methoxybenzyl ethers

A highly selective and efficient method for the unmasking of p-methoxybenzyl (PMB) ethers and esters has been developed by use of 20 mol % of zirconium(IV) chloride as Lewis acid in acetonitrile. The present method is very fast, and the conditions are tolerable to a variety of acid/base-sensitive protecting groups and substrates such as carbohydrates, terpenes, and amino acids. The products are obtained in good to high yields.     

An efficient and chemoselective deprotection of aryl- and styrenyldithioketals (acetals)

In this Letter, an efficient and chemoselective deprotection of aryl- and styrenyldithioketals (acetals) is described. After being carefully examined, 10% Pd/C and Amberlite 120 in refluxing methanol was found to be an excellent condition for the chemoselective deprotection of aryl- and styrenyldithioketals (acetals) in good yields. Under this condition, no deprotection and no reduction of alkyldithioketals (acetals) was observed.     

P(i-BuNCH2CH2)3N: an efficient promoter for the nucleophilic aromatic substitution reaction of aryl fluorides with aryl TBDMS (or TMS) ethers

[reaction: see text]. The nucleophilic aromatic substitution reaction between electron-deficient aryl fluorides and aryl TBDMS (or TMS) ethers has been shown to be efficiently promoted by proazaphosphatranes such as P(i-BuNCH(2)CH(2))(3)N (3). Excellent yields of diaryl ether products were obtained under unusually mild conditions.     

Tetraethylammonium tetraselenotungstate: a new and efficient selenium transfer reagent for the chemoselective synthesis of functionalised diselenides

A variety of functionalised organodiselenides were prepared in excellent yields from the corresponding halides and activated alcohols on treatment with tetraethylammonium tetraselenotungstate 1 under very mild conditions.     

Highly efficient and chemoselective cleavage of prenyl ethers using ZrCl4/NaBH4

An efficient and chemoselective deprotection of prenyl ethers of phenols and alcohols with ZrCl₄/NaBH₄ in DCM was achieved in high yields. The selectivity of prenyl ether deprotection is well demonstrated by carrying out the reaction in the presence of several other ether and ester functionalities.     

A facile zirconium(IV) chloride catalysed selective deprotection of t-butyldimethylsilyl (TBDMS) ethers

A simple and efficient protocol for the selective deprotection of t-butyldimethylsilyl (TBDMS) ethers using 20 mol% ZrCl₄ in 20-45 min and in high yields, is reported, wherein it is demonstrated that acid and base sensitive groups and allylic and benzylic groups are unaffected.     

A mild, efficient, and selective deprotection of tert-butyldimethylsilyl (TBDMS) ethers using dicationic ionic liquid as a catalyst

Selective deprotection of alkyl TBDMS ether in the presence of phenolic TBDMS ether using dicationic ionic liquid [tetraEG(mim)₂][OMs]₂ as a homogeneous catalyst showed significant catalytic activity in methanol at ambient temperature to produce respective alcohol in excellent yield. The present environmentally benign catalytic system is found to be very convenient, fast, high yielding, and clean method for selective desilylation of alkyl silyl ethers even in the existence of other sensitive organic functional groups such as aldehyde, methoxy, and acetate were also achieved.     

An efficient BINAM-copper(II) catalyzed Ullmann-type synthesis of diaryl ethers

A wide range of diaryl ethers are synthesized from the corresponding aryl iodides and phenols through Ullmann type coupling reactions in the presence of a catalytic amount of easily available BINAM-Cu(OTf)₂ complex under mild reaction conditions. Less reactive aryl bromides have also been shown to react with phenols under identical reaction conditions to give good yields of the diaryl ethers without increasing the reaction temperature and time.     

Tetrabutylammonium phthalimide-N-oxyl: An efficient organocatalyst for trimethylsilylation of alcohols and phenols with hexamethyldisilazane

Tetrabutylammonium phthalimide-N-oxyl (TBAPINO) was found to be an effective organocatalyst for rapid, simple and chemoselective protection of the hydroxyl group of alcohols and phenols using hexamethyldisilazane (HMDS) under mild conditions. The low catalyst loading, high to quantitative yields and simple removal of the catalyst from the reaction mixture illustrate the other attractive features of this protocol.