Cleavage of benzyl ethers by triphenylphosphine hydrobromide

Triphenylphosphine hydrobromide was found to cleave the benzyl ethers derived from 1°, 2° alkyl, and aryl alcohols to the corresponding alcohols and benzyltriphenylphosphonium bromide in good yields. Alkene and allyl phosphonium salts were produced from the benzyl ethers with 3° alkyl and allyl groups, respectively. These results indicate that the formation of the product is determined by the relative stability of the carbocationic intermediate. The anhydrous, stoichiometric amount of PPh₃·HBr offers a new and effective method for the deprotection of benzyl ethers.     

Hydrosilylation of Allyl Ethers in the Presence of Platinum(II) Immobilized on Polymethylene Sulfide

Russian Journal of General Chemistry - The reactions of allyl ethyl, allyl butyl, allyl glycidyl, allyl benzyl, and allyl phenyl ethers with 1,1,3,3-tetra-methyldisiloxane in the presence of...     

Synthesis of alkynyl ethers and low-temperature sigmatropic rearrangement of allyl and benzyl alkynyl ethers

Alpha-alkoxy ketones 3 can be transformed into 1-alkynyl ethers 5 by a two-step procedure involving formation of the enol triflate or phosphate and base-induced elimination. Performing the same reaction sequence with allylic alcohols (R2OH, R2 = allyl) furnishes instead gamma,delta-unsaturated carboxylic acid derivatives 6, derived from [3,3]-sigmatropic rearrangement of the intermediate allyl alkynyl ethers at -78 degrees C and trapping of the subsequently formed ketene with nucleophiles (Nu-H). Benzyl alkynyl ether 5 (R2 = benzyl) rearranges to indanone 7 upon heating to 60 degrees C.     

Tautomerism and Stereodynamics of Indophenols,Amidines, Their Derivatives,and Analogs: XIII. Intramolecular Cyclization of 2,6-Di-tert-butyl-4- (o-alkoxyphenylimino)-2,5-cyclohexadienones as a Method of Synthesis of Spiro Benzoxazines

A new method was developed for synthesizing benzoxazine derivatives by O-alkylation of 2,6-di-tert-butyl-4-(o-hydroxyphenylimino)-2,5-cyclohexadienones with allyl or benzyl halides and subsequent thermal heterocyclization of allyl or benzyl ethers thus formed. The cyclization of ethers derived from 2,6-di-tert-butyl-4-(o-hydroxyphenylimino)-2,5-cyclohexadienones and phenacyl bromides or diethyl bromomalonate is so fast that these compounds cannot be isolated.     

Trialkylsilyl triflimides as easily tunable organocatalysts for allylation and benzylation of silyl carbon nucleophiles with non-genotoxic reagents

Trialkylsilyl triflimides generated in situ are unique catalysts for the electrophilic benzylation or allylation of trialkylsilylenol ethers or allyl trialkylsilanes with non-genotoxic alkylating reagents such as benzyl and allyl acetates. In most cases the reactions are fast at room temperature and yields are high. The reaction works particularly well with electron-rich benzyl donors including derivatives of pyrrole, indole and furane.     

Oxidation of Unsaturated Ethers with the System Aluminum Tri-tert-butylate-tert-Butyl Hydroperoxide

The system aluminum tri-tert-butylate-tert-butyl hydroperoxide oxidizes alkyl allyl and aryl allyl ethers by the radical mechanism at room temperature. In the process, either the substrate skeleton is preserved and the carbonyl and hydroperoxy groups are introduced, or the carbon-carbon and carbon-oxygen bonds in the allyl moiety are cleaved. In allyl benzyl ether the reaction centers are the methylene groups of the benzyl and allyl fragments.     

Elaboration of the ether cleaving ability and selectivity of the classical Pearlman's catalyst [Pd(OH)2/C]: concise synthesis of a precursor for a myo-inositol pyrophosphate

The cleavage of propargyl, allyl, benzyl, and PMB ethers by Pd(OH)₂/C can be tuned in that order, by varying the reaction conditions. Other moieties such as C-C double bonds, esters, trityl ether, p-bromo and p-nitrobenzyl ethers are stable to these reaction conditions. Cleavage of allyl ethers can be made catalytic by using 1:1 mixture of Pd(OH)₂/C and Pd/C. The synthetic potential of the selective ether cleaving ability of Pd(OH)₂/C, essentially under neutral conditions, has been demonstrated by an efficient synthesis of a precursor for the preparation of an inositol pyrophosphate derivative.     

A facile and catalytic method for selective deprotection of tert-butyldimethylsilyl ethers with copper(II) bromide

Copper(II) bromide is found to be a simple and efficient catalyst for selective deprotection of tert-butyldimethylsilyl ethers of alcohols/phenols at ambient temperature. Various labile functional groups such as ketal, alkene, ketone, OTBDPS, OTHP and allyl and benzyl ethers are found to be compatible under the reaction conditions.     

Mild, efficient and rapid O-debenzylation of ortho-substituted phenols with trifluoroacetic acid

The mild and efficient deblocking of aryl benzyl ethers with TFA is reported. Cleavage was fastest with ortho-electron-withdrawing groups on the phenolic ring, which we have attributed to a proton chelation effect, furnishing the deprotected phenols in excellent yields. The corresponding para-methoxybenzyl, allyl and iso-propyl ethers were also cleanly removed under these conditions. In addition, the selective aryl benzyl ether debenzylation in the presence of benzyl ester, Cbz carbamate and Boc carbamate functionalities was also observed.     

A hierarchy of aryloxide deprotection by boron tribromide

Aryl propargyl ethers and esters are cleaved selectively in the presence of aryl methyl ethers and esters by boron tribromide in dichloromethane. Under the same conditions, allyl ethers undergo very rapid Claisen rearrangement, and benzyl ethers are also cleaved more rapidly than propargyl. A mechanism involving intramolecular delivery of bromide to the propargyl terminus is proposed. [reaction: see text]     

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.     

Selective electrochemical deprotection of cinnamyl ethers, esters, and carbamates

Electrochemical deprotection of the cinnamyl moiety from ethers, esters, and carbamates was studied with the focus on O- versus N- selectivity as well as selectivity over allyl or benzyl systems.     

Oxovanadium(V)-Catalyzed Deoxygenative Coupling Reaction of Alcohols with Trimethylsilyl Enol Ethers in the Presence of MS3A

Oxovanadium(V)-catalyzed deoxygenative coupling reaction of allyl alcohols with trimethylsilyl enol ethers was demonstrated to afford γ,δ-unsaturated carbonyl compounds in one-step. The catalytic deoxygenative coupling reaction of allyl alcohols proceeded smoothly with both aromatic and aliphatic trimethylsilyl enol ethers. This catalytic deoxygenative coupling system could be applied to the deoxygenative coupling reaction of benzyl alcohols with trimethylsilyl enol ethers, providing the corresponding carbonyl compounds. Furthermore, a gram-scale catalytic synthesis of the γ,δ-unsaturated carbonyl compound was successfully performed to validate the scalability of this catalytic deoxygenative coupling reaction.     

Computational study of the thermal decomposition and the thermochemistry of allyl ethers and allyl sulfides

In spite of the several experimental and computational studies on the thermal decomposition of allyl ethers and allyl sulfides, there are still disagreements on aspects of the reaction mechanism, such as the true nature of the transition states and the grade of synchronicity of the reactions. This work presents a computational study of the gas-phase thermolysis reaction of allyl ethers and allyl sulfides substituted at α-carbon, at the M05-2X/6-31+G(d,p) level of theory and a temperature range from 586.15 to 673.15 K. The substituent groups were methyl, ethyl, n-propyl, i-propyl, allyl, benzyl and acetonyl. It was found that the sulfides react faster than the homologous ethers and that the substituent groups with the capacity of delocalize charge increase the reaction rate. Through natural bond orbital calculations, the transition states were characterized. The synchronicities and atomic charges of the studied reactions were determined. A computational study at the G3 level of theory on the thermochemistry of allyl ethers and sulfides was also carried out.     

Propargyloxycarbonyl (Poc) as a protective group for the hydroxyl function in carbohydrate synthesis

[reaction: see text] The propargyloxycarbonyl (Poc) group can be used for the selective protection of the hydroxyl function in carbohydrates and can be removed under neutral conditions using tetrathiomolybdate MoS(4)(2-) (1) in CH(3)CN at room temperature. Under the conditions of deprotection benzylidine acetals, benzyl ethers, acetyl and levulinoyl esters, and allyl and benzyl carbonates are left untouched. It has also been shown that the new protective group (Poc) is compatible with acidic, basic, and also glycosylation conditions.     

Oxidation of acyclic alkenes and allyl and benzyl ethers with DIB/t-BuOOH/Mg(OAc)2

Oxidation of (11Z)-1′,2′-didehydrostemofoline with DIB/TBHP/Mg(OAc)₂·4H₂O resulted in oxidative cleavage of the C-11–C-12 double bond instead of the desired allylic oxidation of the 1-butenyl side chain. Stemofoline gave a similar result. The oxidation of more simple terminal alkenes was regioselective and gave vinyl ketones while allyl and benzyl ethers gave acrylate and benzoate esters, respectively. Allyl and benzyl ethers could be chemoselectively oxidized in the presence of a terminal alkene or benzyl group. Oxidation of an internal alkene was poorly regioselective, in contrast to the oxidation of 1-substituted cyclohexenes.     

Synthesis of isochromene and related derivatives by rhodium-catalyzed oxidative coupling of benzyl and allyl alcohols with alkynes

The straightforward synthesis of isochromene derivatives and related cyclic ethers is achieved by the rhodium-catalyzed oxidative coupling of α,α-disubstituted benzyl and allyl alcohols with alkynes. The hydroxy groups effectively act as the key function for the regioselective C-H bond cleavage.     

NbCl5 mediated deprotection of methoxy methyl ether

An efficient cleavage of methoxy methyl ether using NbCl₅ is described. This protocol works efficiently with MOM ethers of alkyl, allyl, propargyl, benzyl alcohol and phenol derivatives. MOM esters are also found to be effectively cleaved under the present conditions.     

Thiol‐ene clickable hyperscaffolds bearing peripheral allyl groups

Radical catalyzed thiol‐ene reaction has become a useful alternative to the Huisgen‐type click reaction as it helps to expand the variability in reaction conditions as well as the range of clickable entities. Thus, direct generation of hyperbranched polymers bearing peripheral allyl groups that could be clicked using a variety of functional thiols would be of immense value. A specifically designed AB₂ type monomer, that carries two allyl benzyl ethers groups and one alcohol functionality, was shown to undergo self‐condensation under acid‐catalyzed melt‐transetherification to yield a hyperbranched polyether that carries numerous allyl end‐groups. Importantly, it was shown that the kinetics of polymerization is not dramatically affected by the change of the ether unit from previously studied methyl benzyl ether to an allyl benzyl ether. The peripheral allyl groups were readily clicked quantitatively, using a variety of thiols, to generate an hydrocarbon‐soluble octadecyl‐derivative, amphiphilic systems using 2‐mercaptoethanol and chiral amino acid (N‐benzoyl cystine) derivatized hyperbranched structures; thus demonstrating the versatility of this novel class of clickable hyperscaffolds. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Improved procedure for the synthesis of gem-diiodoalkanes by the alkylation of diiodomethane. scope and limitations

Functionalized gem-diiodoalkanes are obtained in good to excellent yields by employing a convenient modified procedure for the alkylation of NaCHI2 with alkyl iodides. Complete conversion to the diiodide is reliably obtained, avoiding a problematic separation of any remaining iodide starting material. Functional group tolerance toward olefins, acetals, ethers and silyl ethers, carbamates, and hindered esters is demonstrated. The use of an excess of LiCHI2 allows complete conversion of allyl and benzyl bromides with minimal elimination from the diiodide product.