A new method for the deprotection of benzyl ethers or the selective protection of alcohols

A new selective method for the deprotection of benzyl ethers situated next to alcohols in the alpha, beta, or gamma position is presented which uses either NIS or DIB/I2 as a reagent. After initial formation of a hypoiodite intermediate, the reaction is believed to follow a radical pathway to resemble the Hoffman-Loffler-Freytag reaction. The formation of the intermediate hypoiodite is suggested on the basis of NMR studies. Depending on the substrate, the corresponding benzylidene derivatives or diols are isolated.     

A mild and selective method for the N-Boc deprotection by sodium carbonate

A cleavage of N-tert-butyloxycarbonyl protection by Na₂CO₃ is reported. The N-free products are obtained in excellent yields. The compatibility of the method with the presence of acidic or basic groups is demonstrated. The reactions were performed on indole, azaindole, indazole, pyrazole, indolinone, quinolinone, and oxazolone.     

A mild copper catalyzed method for the selective deprotection of aryl allyl ethers

Copper boryl reagents enable the selective cleavage of aryl allyl ethers to the corresponding phenols in good to moderate yields.     

A mild and efficient approach for the selective deprotection of benzyl and phenyl trimethylsilyl ethers in 1-butyl-3-methyl-imidazolium chloride

1-Butyl-3-methyl-imidazolium chloride ([bmim]Cl) in the absence of any catalyst mediated the selective deprotection of benzyl and phenyl trimethylsilyl (TMS) ethers to the corresponding alcohols and phenol in good yields at room temperature even in presence of alkyl silyl ethers. The work-up of reactions is very simple and the products do not require further purification. The ionic liquid (IL) can be recycled and reused for several runs without any significant loss of activity.     

A mild and efficient approach for the selective deprotection of benzyl and phenyl trimethylsilyl ethers in 1-butyl-3-methyl-imidazolium chloride

1-Butyl-3-methyl-imidazolium chloride ([bmim]Cl) in the absence of any catalyst mediated the selective deprotection of benzyl and phenyl trimethylsilyl (TMS) ethers to the corresponding alcohols and phenol in good yields at room temperature even in presence of alkyl silyl ethers. The work-up of reactions is very simple and the products do not require further purification. The ionic liquid (IL) can be recycled and reused for several runs without any significant loss of activity. Correspondence: Ahmad Shaabani, Department of Chemistry, Shahid Beheshti University, PO Box 19396-4716, Tehran, Iran.     

A facile method for deprotection of O-allylphenols

Allyl aryl ethers can be easily cleaved by the use of 10% Pd/C under the mild and basic conditions.     

The mass spectra of some benzyl esters and thioethers

The electron impact mass spectra of a large number of benzyl esters of carboxylic acids are reported. The fragmentation behaviour is discussed and the esters are divided into groups according to structure and fragmentation. For most esters benzylic cleavage with H transfer competes with simple cleavage.     

Novel deprotection of SEM ethers: A very mild and selective method using magnesium bromide

New lability and stability sequences have been established for multifunctional substrates containing SEM ether group(s) by a MgBr(2)/Et(2)O/MeNO(2) deprotection protocol.     

CpRuIIPF6/quinaldic acid-catalyzed chemoselective allyl ether cleavage. A simple and practical method for hydroxyl deprotection

A cationic CpRu(II) complex in combination with quinaldic acid shows high reactivity and chemoselectivity for the catalytic deprotection of hydroxyl groups protected as allyl ethers. The catalyst operates in alcoholic solvents without the need for any additional nucleophiles, satisfying the practical requirements of operational simplicity, safety, and environmental friendliness. The wide applicability of this deprotection strategy to a variety of multifunctional molecules, including peptides and nucleosides, may provide new opportunities in protective group chemistry. [structure: see text]     

A mild and efficient method for the chemoselective deprotection of acetonides with lanthanum(III) nitrate hexahydrate

Acetonides are hydrolyzed selectively and efficiently with lanthanum(III) nitrate hexahydrate in acetonitrile. The method has good compatibility with other sensitive hydroxyl protecting groups such as trityl, TBDMS, THP, OAc, OBz and OBn.     

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.     

An exceptionally mild deprotection of phthalimides

Phthalimides are converted to primary amines in an efficient, two-stage, one-flask operation using NaBH₄/2-propanol, then acetic acid.     

A mild Boc deprotection and the importance of a free carboxylate

We report a facile and rapid removal of Boc protecting groups using microwave heating in H₂O, with deprotection only requiring a free carboxylic acid group in the starting material. Unlike previous approaches, no additional reagents are required.     

A method for the reductive scission of heterocyclic thioethers

A mild, chemoselective, and generally high-yielding method for the reductive scission of heterocyclic thioethers is described. Suitable heterocycles have a thioether substituent at the 2-position relative to a ring heteroatom. The convenient and straightforward method is demonstrated with reactants which are not compatible with the standard Raney nickel conditions such as sulfides, sulfones, and thiophenes. In addition, benzyl esters, benzyl amides, and benzyl carbamates are tolerated by the reductive reaction conditions.     

A mild and efficient method for the selective deprotection of silyl ethers using KF in the presence of tetraethylene glycol

A mild and efficient protocol for the deprotection of silyl ethers using KF in tetraethylene glycol is reported. A wide range of alcoholic silyl ethers can be selectively cleaved in high yield in the presence of certain acid- and base-labile functional groups. Moreover, the phenolic silyl ethers were cleaved exclusively, without affecting the alcoholic silyl ethers, at room temperature.     

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.     

A method for the deprotection of alkylpinacolyl boronate esters

A two-step procedure for deprotection of alkylpinacolyl boronate esters via transesterification with diethanolamine followed by hydrolysis was successfully developed with the advantages of tolerance to various functional groups, short reaction time, and ease of product isolation.     

A mild deprotection strategy for allyl-protecting groups and its implications in sequence specific dendrimer synthesis

A mild deprotection strategy for allyl ethers under basic conditions in the presence of a palladium catalyst is described. Under these conditions, aryl allyl ethers can be cleaved selectively in the presence of alkyl allyl ethers. These conditions are also effective in the deprotection of allyloxycarbonyl groups. The utility of the current methodology in sequence specific dendrimer synthesis is demonstrated.     

Reductive demercuration in deprotection of trityl thioethers, trityl amines, and trityl ethers.

A room-temperature deprotection method of trityl amines, -ethers, and -thioethers is presented, based on coupling of metal acid catalysis (HgX(2), with X(-) = Cl(-) or OAc(-)) and sodium borohydride reduction. The results of its application to monotritylated compounds (ethanethiol, ethanol, and piperidine) and to mono- and ditritylated 1,2-bifunctional compounds (mercaptoethanol, aminoethanethiol, and ethanolamine) are compared with those obtained with early methods based on the use of strong Br?nsted acids (pure TFA and MeCN solutions of HCl). Trityl thioethers of simple thiols and amino and hydroxy thiols are promptly cleaved by reductive detritylation, and one-pot procedures can be employed to produce free thiols. In contrast, dilution with water of these same compounds in solutions of strong Br?nsted acids leaves them unaffected. O-Tr and N-Tr bonds are broken by this latter treatment. However, trityl ethers are rapidly cleaved by even dilute HCl solutions, while cleaving of trityl amines is modulated by HCl concentration. Addition of NaBH(4) to solutions of monofunctional trityl ethers in HgCl(2)/MeCN leads to complete deprotection. Monofunctional trityl amines are partially deprotected only if the complexation reaction is allowed to reach equilibrium. Combination of H(+)- with HgX(+)-catalyzed detritylation methods allows selective deprotection of pertritylated amino and hydroxy thiols. The results appear to be due to the strong difference in the affinity of the donor atoms present in the pertritylated substrates for H(+) and HgX(+). Catalysis based on Br?nsted acids leads to cleaving of the N- and O-trityl bonds with recovering of the S-trityl group; that based on mercury salts allows recovering of N- and O-trityl groups with deprotection of the -SH function. Selectivity in deprotection of pertritylated amino alcohols seems to be severely hampered by similarity in the affinity of N- and O-atoms for H(+) and HgX(+), and, taking advantage of the lower HgX(+)-complexation rate of the N-trityl with respect to the O-trityl group, only preservation of the N-trityl bond has been achieved.     

Solid-supported acids as mild and versatile reagents for the deprotection of aromatic ethers

p-Toluene sulfonic acid (p-TsOH) immobilized either on polystyrene (PS) or silica (Si) was found to be effective in cleaving aromatic ethers containing isopropyl, tert-butyl, allyl, and benzyl groups, as well as mono-, di-, and trimethoxylated benzyl groups, in moderate to excellent yields (54-95%). These protecting groups could be selectively deprotected when they were simultaneously present on the same or different aromatic rings in a substrate.