Rearrangements of organometallic compounds : X. The mechanism of 1,2-aryl migration in the Wittig rearrangement of α-metallated benzyl aryl ethers

The mechanism of 1,2-aryl shifts in the Wittig rearrangement of α-metallated benzyl aryl ethers has been investigated by a detailed examination of the behavior of the following ethers: benzyl phenyl ether, benzyl para-tert-butyl- and meta-tert-butyl-phenyl ethers, benzyl 2-bromo-4-tert-butylphenyl ether and dibenzo[b,d] pyran. The failure to trap any aldehyde intermediate, the ease of rearrangement for the pyran, the lack of evidence for an aryne intermediate with the benzyl butyl ethers and other circumstantial evidence have led to the proposal of an intramolecular pathway in which radical pairs are generated and then collapse to the isomeric carbinolate.     

One-Pot Reductive Mono-N-alkylation of Aromatic Nitro Compounds Using Nitriles as Alkylating Reagents

Palladium catalysed transfer hydrogenation using cyclohexene as the donor is found to deprotect readily alcohol benzyl ethers and aliphatic benzyl esters. The phenol benzyl ethers and benzyl benzoates are stable under these conditions.     

Chemoselective and Direct Functionalization of Methyl Benzyl Ethers and Unsymmetrical Dibenzyl Ethers by Using Iron Trichloride

Methyl and benzyl ethers are widely utilized as protected alcohols due to their chemical stability, such as the low reactivity of the methoxy and benzyloxy groups as leaving groups under nucleophilic conditions. We have established the direct azidation of chemically stable methyl and benzyl ethers derived from secondary and tertiary benzyl alcohols. The present azidation chemoselectively proceeds at the secondary or tertiary benzylic positions of methyl benzyl ethers or unsymmetrical dibenzyl ethers and is also applicable to direct allylation, alkynylation, and cyanation reactions, as well as the azidation. The present methodologies provide not only a novel chemoselectivity but also the advantage of shortened synthetic steps, due to the direct process without the deprotection of the methyl and benzyl ethers.     

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.     

Selective catalytic activity of ball-shaped Pd@MCM-48 nanocatalysts

Remarkable selectivity is achieved in the cleavage of benzyl ethers using ball-shaped palladium nanocatalysts, Pd@MCM-48, in an MCM-48 matrix. The unique nanocatalysts not only feature unprecedented complete hydrogenolysis selectivity of a benzyl ether over hydrogenation of a double bond, but also demonstrate selective cleavage of unsubstituted benzyl ether over substituted benzyl ethers.     

Synthesis of Benzyl Alkyl Ethers by Intermolecular Dehydration of Benzyl Alcohol with Aliphatic Alcohols under the Effect of Copper Containing Catalysts

Synthesis of benzyl alkyl ethers was performed in high yields by intermolecular dehydration of benzyl and primary, secondary, tertiary alcohols under the effect of copper containing catalysts. The formation of benzyl alkyl ethers occurs with participation of benzyl cation.     

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.     

Iodine-catalyzed one-pot three-component synthesis of homoallyl benzyl ethers from aldehydes

Iodine has been found to be an effective catalyst for one-pot synthesis of homoallyl benzyl ethers under mild reaction conditions. Various homoallyl benzyl ethers were synthesized in moderate to high yield by three-component condensation of aldehydes, benzyloxytrimethylsilane, and allyltrimethylsilane in presence of iodine (10 mol %) in dichloromethane at 0 °C.     

Selective Deprotection of tert -Butyldimethylsilyl Ethers Using Nafion-H®/Sodium Iodide (or Bromodimethylsulfonium Bromide) in Methanol

Abstract

Catalytic amounts of bromodimethyl sulfonium bromide, or Nafion-H along with NaI (1 equiv.), in methanol cleave a variety of TBDMS ethers readily in high yields. Alkyl TBDMS ethers react more readily and selectively compared to phenolic TBDMS ethers, benzyl, and methyl ethers.     

氯化铵三氧化铬在干反应中对苄醚的选择性氧化

本文报道氯化铵三氧化铬(ACC)是具有高选择性的氧化剂, 在无溶剂的干反应中, 可以把苄醚氧化成相应的苯甲酸酯, 且顶点满意的产率.     

Halogen-lithium exchange versus deprotonation: synthesis of diboronic acids derived from aryl-benzyl ethers

Lithiation of a series of aryl benzyl ethers containing halogen substituents (-F, -Br, -I) was investigated. The resultant mono- and diorganolithium intermediates were converted into the corresponding aldehydes or diboronic acids in good yields. The dilithiation of aryl benzyl ethers containing a reactive hydrogen atom and halogen atom capable of halogen-lithium exchange proceeds quantitatively in THF at −50 °C. It was found that mono aryllithiums formed in the reaction can remove the reactive hydrogen atom from a molecule of aryl benzyl ether thus decreasing the yield of dilithiated species. This effect does not occur when t-BuLi is used instead of n-BuLi.     

Use of Ferric Chloride in Carbohydrate Reactions.1 Iv. Acetolysis of Benzyl Ethers of Sugars

Acetolysis of benzyl ethers of sugars has been carried out with anhydrous ferric chloride in acetic anhydride. By employing this reagent, benzyl ether groups variously placed in sugars or in their glycosides could be removed with ease and replaced by acetyl groups. By controlled acetolysis, preferential removal of certain benzyl groups was possible. The results show that in D-glucose the relative ease of removal of benzyl ether groups by acetolysis follows the order C-6 > C-4 > C-3 > C-2 and that the rate of acetolysis is 6-O-Bn : 3-O-Bn : 2-O-Bn = 125 : 24 : 1. The corresponding methyl ethers were very sluggish towards acetolysis.     

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.     

A convenient procedure for the synthesis of allyl and benzyl ethers from alcohols and phenols

Allyl and benzyl ethers of alcohols can be prepared conveniently and in high yield with allyl and benzyl bromide in the presence of solid potassium hydroxide without use of any solvent. Phenols can be converted to allyl ethers but are inert to benzylation under above conditions.     

New convergent one pot synthesis of amino benzyl ethers bearing a nitrogen-containing bicycle

We report herein a new convergent one pot method for the synthesis of amino benzyl ethers containing a bicyclic amine, derived from different substituted benzyl alcohols and bicyclic amino alcohols such as tropine, pseudotropine, and 3-quinuclidinol, using chlorotrimethylsilane and sodium iodide. In order to avoid the competitive reaction with the nitrogen atom, a solution of the separately prepared alkoxide of tropine, pseudotropine, and 3-quinuclidinol was added to the preformed substituted benzyl iodides and allowed to reflux at 90?°C for 15?h under nitrogen atmosphere. This method provides an efficient alternative of the preparation of amino benzyl ethers in organic synthesis with good yields in comparison with existed methods.     

Simple,High Yield Preparation of N-Benzylacetamides by Lewis Acid-Catalyseed Reaction of Benzyl Chlorides or Benzyl Methyl Ethers with Acetonitrile

Reaction of either benzyl chlorides or benzyl methyl ethers with hydrated ferric chloride in acetonitrile results in smooth Ritter reaction and formation of N-benzylacetamides in excellent yield.     

Pd-catalyzed one-pot chemoselective hydrogenation protocol for the preparation of carboxamides directly from azides

Carboxamides were obtained efficiently in high yields from azides on reaction with the corresponding pre-formed activated carboxylic acids in a single-step reductive transformation using hydrogen atmosphere (balloon) under Pd/BaSO₄ or Pd/CaCO₃ catalysis. The method is highly chemoselective and compatible with extremely labile functional groups such as benzyl carbamates, benzyl ethers, benzyl esters, and olefins.     

Reduction of carbon-carbon double bonds and hydrogenolysis by sodium hypophosphite

Sodium hypophosphite plus palladium-charcoal is a mild, economical, selective system for the reduction of carbon-carbon double bonds and hydrogenolysis of benzyl ethers and benzyl carbonates.     

苄基醚选择性间接电氧化的研究

以Mn(Ⅲ) / Mn(Ⅱ)为 间接氧化还原体系研究苄基醚的氧化. 实验结果表明该体系能高产率选择性地氧化苄基醚为 苯甲醛和相应的醇. 阳极液中Mn(Ⅱ)可以循环使用.     

Safe radical azidonation using polystyrene supported diazidoiodate(I)

Aldehydes are converted to acyl azides and benzyl ethers to azido ethers by treatment with polymer supported iodine azide in MeCN at 83 °C. The reaction provides a safe and convenient alternative to the use of iodine azide in radical azidonations.