SYNTHESIS OF ALKYL AND ARYL 1-PROPENYL ETHER MONOMERS: A NEW APPROACH

A new, convenient synthesis of alkyl and aryl 1-propenyl ether monomers in good to excellent yields has been developed. Alkyl and aryl allyl ethers can be smoothly isomerized to the desired 1-propenyl ethers by refluxing in a basic ethanolic solution containing pentacarbonyliron as a catalyst. A simplified two-step, one-pot procedure has also been developed which consists of combining an alcohol with allyl bromide in the presence of base and then adding pentacarbonyliron to isomerize the in-situ generated allyl ether to directly give the 1-propenyl ether. Good yields of alkyl 1-propenyl ethers were obtained using this process. Factors affecting the isomerization reaction were investigated and a mechanism was proposed.     

Stereoselective Isomerization of Unsymmetrical Diallyl Ethers to Allyl (E)-Vinyl Ethers by a Cationic Iridium Catalyst

The stereoselective isomerization of unsymmetrical diallyl ethers to allyl (E)-vinyl ethers was carried out in the presence of a cationic iridium(I) catalyst. The catalyst prepared in situ by treating [Ir(cod)(PPh₂Me)₂]PF₆ with hydrogen was found to be an excellent catalyst to selectively isomerize the less substituted allyl group to an (E)-vinyl ether.     

Cleavage of different ether bonds in butyl glycidyl ether and allyl glycidyl ether by K, K(15-crown-5)2

The kind of substituent in alkyl glycidyl ethers affects the course of their reaction with K⁻, K⁺(15-crown-5)₂. The cyclic oxirane ring is exclusively cleaved in the case of butyl glycidyl ether whereas the presence of the unsaturated allyl group in the glycidyl ether molecule unexpectedly prefers the scission of the linear ether bond. In both the systems organometallic intermediates are formed. They react with crown ether causing its ring opening. Allylpotassium formed from allyl glycidyl ether reacts also with another glycidyl ether molecule; the oxirane ring is opened in this case.     

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.     

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.     

Synthesis of allyl and alkyl vinyl ethers using an in situ prepared air-stable palladium catalyst. Efficient transfer vinylation of primary,secondary, and tertiary alcohols

An air-stable palladium catalyst formed in situ from commercially available components efficiently catalyzed the transfer vinylation between butyl vinyl ether and various allyl and alkyl alcohols to give the corresponding allyl and alkyl vinyl ethers in 61-98% yield in a single step.     

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.     

Substituent effects on the rate constants for the photo-Claisen rearrangement of allyl aryl ethers

The photochemistry of 11 substituted allyl 4-X- and 3-X-aryl ethers 3 (ArOCH2-CH=CH2) has been examined in both methanol and cyclohexane as solvents. The ethers react by the photo-Claisen rearrangement to give allyl substituted phenols as the major primary photoproducts, as expected from the well-established radical pair mechanism. The excited singlet state properties (absorption spectra, fluorescence spectra, fluorescence quantum yields, and singlet lifetimes) were compared with a parallel set of unreactive 4-X- and 3-X-anisoles 4. The excited-state properties of three substituted 4-X-aryl 4-(1-butenyl) ethers 14 (ArOCH2CH2-CH=CH2) were also examined. The model compounds 4 and the reactive allyl ethers 3 have essentially identical rate constants for the excited-state processes with the exception of, the rate constant for homolytic cleavage from S(1) of the allyl ethers to give the radical pair. The difference between the fluorescence quantum yields and/or singlet lifetimes for 3 and 4 were used to obtain values of for all of the allyl ethers. These values exhibit a large substituent effect, spanning almost 2 orders of magnitude with electron-donating groups (CH3O, CH3) accelerating the reaction and electron-withdrawing ones (CN, CF3) slowing it down. The parallel range of rate constants observed in both methanol and cyclohexane indicates that ion pairs are not important intermediates in these rearrangements. Quantum yields of reaction (Phi(r)) for several of the more reactive ethers demonstrate that neither these values nor rate constants of reaction derived from them are reliable measures of the actual excited-state process. In fact, the values are significantly lower than the ones, indicating that the radical pairs undergo recombination to generate starting material. Finally, the rate constants were found to parallel a trend for the change in bond dissociation energy (deltaBDE) for the O-C (allyl) bond of the allyl ethers, indicating that other possible substituent effects are of minor importance.     

Transition metal-catalyzed isomerization and polymerization of allylic and enolic ethers

Alkyl allyl ethers undergo facile thermally induced isomerization to alkyl 1-propenyl ethers in the presence of Group VIII transition metal carbonyl compounds as catalysts. The addition of a silane containing a Si H bond to these systems results in a catalyst system that is capable of not only isomerizing the allyl ether to the 1-propenyl ether, but further results in the polymerization of these later compounds. High molecular weight polymers can be obtained directly from the alkyl allyl ether in a single step. The scope and limitations of these polymerizations are described. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2521–2532, 1997     

Regioselective Alkoxyiodination of Allyl Ethers in Unsaturated C3-Alcohols

Russian Journal of Organic Chemistry - Alkoxyiodination of alkyl allyl ethers with elemental iodine in allyl and propargyl alcohols in the presence of clinoptilolite [(NaK)4CaAl6Si30O72] gave the...     

Allylation of alcohols and carboxylic acids with allyl acetate catalyzed by [Ir(cod)2](+)BF4- complex

A facile method for the synthesis of allyl alkyl ethers from alcohols with allyl acetate was developed by the use of [Ir(cod)(2)](+)BF(4)(-) complex. For instance, the reaction of allyl acetate with n-octyl alcohol in the presence of a catalytic amount of [Ir(cod)(2)](+)BF(4)(-) complex afforded allyl octyl ether in quantitative yield. Allyl carboxylates were also prepared by the exchange reaction between carboxylic acids and allyl acetate in good yields. The [Ir(cod)(2)](+)BF(4)(-) complex catalyzed the reaction of alkyl and aromatic amines with allyl acetate to lead to the corresponding allylamines in fair to good yields.     

Polymerization of alkyl allyl oxalates in the evolution of carbon dioxide at elevated temperatures

Radical polymerization of several alkyl allyl oxalates, including methyl allyl oxalate (MAO), ethyl allyl oxalate, propyl allyl oxalate, butyl allyl oxalate, and octyl allyl oxalate, was conducted in the evolution of carbon dioxide at elevated temperatures, and was compared with the anomalous polymerization behavior of diallyl oxalate (DAO) discussed in our earlier article

1 A. Matsumoto, I. Tamura, M. Yamawaki, and M. Oiwa, J. Polym. Sci. Polym. Chem. Ed., 17 , 1419 (1979).

. The kinetic equations for the polymerization of alkyl allyl oxalate were derived following the kinetic treatment of the DAO polymerization by further consideration of the absence of cyclization of the growing polymer radical and the effective reinitiation by alkyl radical, and were then satisfactorily applied to the polymerization of MAO, as a representative alkyl allyl oxalate. The evolution of carbon dioxide in the polymerization of alkyl allyl oxalates was enhanced with the increase of bulkiness of the alkyl substituent, as a result of steric suppression of the propagation of the growing polymer radical.     

Relative thermodynamic stabilities of isomeric alkyl allyl and alkyl (Z)-propenyl ethers

The relative thermodynamic stabilities of ten allyl ethers (ROCH₂CH=CH₂) and the corresponding isomeric (Z)-propenyl ethers (where R is an alkyl group, or a methoxysubstituted alkyl group) have been determined by chemical equilibration in DMSO solution with t-BuOK as catalyst. From the variation of the equilibrium constant with temperature, the values of the thermodynamic parameters ΔGΘ, ΔHΘ and ΔSΘ of isomerization at 298.15 K were evaluated. The propenyl ethers are highly favored at equilibrium, the values of both ΔGΘ and ΔHΘ for the allyl → propenyl reaction being ca. −18 to −25 kJ mol⁻¹. The favor of the propenyl ethers is increased by bulky alkyl substituents, and decreased by methoxy-substituted alkyl groups. In most cases the entropy contribution is negligible; however, for R = (MeO)₂CH and R = (MeO)₃C the values of ΔSΘ are ca. −5 J K⁻¹ mol⁻¹.     

Synthesis of Cyclopropyl Ethers and Cyclopropanols by Carbene Transfer – Acetolysis of Cyclopropyl p-Toluenesulfonates

The reaction of chloromethyl phenyl ether with butyllithium in olefins yields phenoxy-cyclopropanes. 1-Chloro-1-phenoxycyclopropanes can be prepared in a similar manner, though the yields are poor. Alkoxycyclopropanes are formed when dichloromethyl alkyl ethers are treated with methyllithium/lithium iodide in the presence of olefins. Cyclopropanols can be obtained in good yields by reaction of (β-chloroethoxy)cyclopropanes either with butyl- or ethyllithium or with bases. – As was shown by acetolysis experiments with cyclopropyl p-toluenesulfonates having a known steric configuration, the rearrangement of a cyclopropyl derivative into an allyl cation proceeds in accordance with the Woodward-Hoffmann-DePuy rule. The solvolysis of exo-bicyclo[n.1.0]alkyl p-toluene-sulfonates is assumed to proceed via “semi-open” intermediates, which are somewhere between an allyl cation and a cyclopropyl cation.     

Ether formation from allylic alcohols catalyzed by samarium trichloride

The behaviour of various allylic alcohols in the presence of catalytic amounts of SmCl₃ (by heating in 1,2-dichloroethane) has been studied. Diallyl ethers are obtained in many cases in good yields. Mixed allyl alkyl ethers are also prepared if 2–5 equivalents of an aliphatic alcohol is present. The reactions are interpreted as proceeding through a pseudo allylic carbonium intermediate initiated by a preliminary complexation of the allyl hydroxyl to the samarium ion.     

Preparation of cyclopropane hydrocarbons via organoaluminum compounds

Summary Cyclopropane hydrocarbons are formed in good yields by the thermal decomposition of the products of the addition of dialkylaluminum hydrides to substituted alkyl allyl ethers.     

Synthesis of Alkyl 4-Ethyn(en)yl-6-methyl-1,3-dioxane-5-carboxylates

Russian Journal of Organic Chemistry - Condensations of chloromethyl propargyl(allyl) ethers with alkyl 3-oxobutanoates in the presence of pyridine gave substituted 1,3-dioxanes.     

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.     

Direct synthesis of ethers from aldehydes and ketones. One-pot reductive etherification of benzaldehydes,alkyl aryl ketones,and benzophenones

Benzyl alcohols formed by the reduction of benzaldehydes, alkyl aryl ketones, and benzophenones with sodium tetrahydridoborate in alcohols undergo in situ etherification with the solvent in the presence of a catalytic amount of HCl. Thus the process may be regarded as one-pot transformation of carbonyl compounds into the corresponding benzyl ethers. The yields of ethers depend on the substituent nature in the aromatic fragment of the initial carbonyl compound and on the alcohol used as reduction medium.     

The Cp2ZrCl2-catalyzed cycloalumination of functionally substituted olefins with triethylaluminum

Reactions of functionally substituted olefins (allylamines, sulfides and ethers, homoallylic alcohols and amines, as well as vinyl ethers) with Et₃Al in the presence of Cp₂ZrCl₂ as a catalyst were studied. Cycloalumination of allylamines occurs with high regioselectivity to furnish after subsequent deuterolysis 4-deutero-2-(deuteromethyl)butyl-substituted amines. Cycloalumination of alkyl allyl sulfide is accompanied by a side process of the C-S bond cleavage. In the case of allyl and vinyl ethers, no cycloalumination products are formed under the reaction conditions. However, the reactions with homoallylic alcohol and amine after deuterolysis gave the corresponding dideutero-containing compounds in good yields.