- Relative Thermodynamic Stabilities of Isomeric Alkyl Allyl and Alkyl (Z)-Propenyl Ethers
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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 ΔG, ΔH and ΔS of isomerization at 298.15 K were evaluated.The propenyl ethers are highly favored at equilibrium, the values of both ΔG and ΔH 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 methoxysubstituted alkyl groups.In most cases the entropy contribution is negligible; however, for R=(MeO)2CH and R=(MeO)3C the values of ΔS are ca. -5 J K-1 mol1-.
- Taskinen, Esko
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- Clean protocol for deoxygenation of epoxides to alkenes: Via catalytic hydrogenation using gold
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The epoxidation of olefin as a strategy to protect carbon-carbon double bonds is a well-known procedure in organic synthesis, however the reverse reaction, deprotection/deoxygenation of epoxides is much less developed, despite its potential utility for the synthesis of substituted olefins. Here, we disclose a clean protocol for the selective deprotection of epoxides, by combining commercially available organophosphorus ligands and gold nanoparticles (Au NP). Besides being successfully applied in the deoxygenation of epoxides, the discovered catalytic system also enables the selective reduction N-oxides and sulfoxides using molecular hydrogen as reductant. The Au NP catalyst combined with triethylphosphite P(OEt)3 is remarkably more reactive than solely Au NPs. The method is not only a complementary Au-catalyzed reductive reaction under mild conditions, but also an effective procedure for selective reductions of a wide range of valuable molecules that would be either synthetically inconvenient or even difficult to access by alternative synthetic protocols or by using classical transition metal catalysts. This journal is
- Fiorio, Jhonatan L.,Rossi, Liane M.
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p. 312 - 318
(2021/01/29)
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- A convenient synthesis of tert-butyl ethers under microwave condition
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Synthesis of tert-butyl ethers from various alcohols and substituted phenols can be achieved using tert-butyl bromide in the presence of basic lead carbonate as a catalyst under microwave irradiation in absence of solvent. The catalyst is easily recovered via filtration and reused up to three times without appreciable loss of activity.
- Mahammed,Keshava Murthy,Mohana Raju
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p. 575 - 578
(2008/09/20)
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- Efficient synthesis of tert-butyl ethers under solvent-free conditions
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A simple and efficient synthesis of tert-butyl ethers from various alcohols and substituted phenols using tert-butyl bromide in the presence of basic lead carbonate as a catalyst. The catalyst is easily recovered via filtration and can be reused up to three times without appreciable loss of activity. Copyright Taylor & Francis Group, LLC.
- Rai, Neithnadka Premsai,Arunachalam, Pirama Nayagam
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p. 2891 - 2896
(2008/02/13)
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- Halide-Free Dehydrative Allylation Using Allylic Alcohols Promoted by a Palladium-Triphenyl Phosphite Catalyst
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The triphenyl phosphite-palladium complex was found to effect catalytic substitution reactions of allylic alcohols via a direct C-O bond cleavage. The dehydrative etherification proceeded efficiently without any cocatalysts and bases to give allylic ethers in good to excellent yields.
- Kayaki, Yoshihito,Koda, Takashi,Ikariya, Takao
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p. 2595 - 2597
(2007/10/03)
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- Rhenium-Catalyzed Epoxide Deoxygenation: Scope and Limitations
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Transfer of oxygen atoms from epoxides to triphenylphosphine is efficiently catalyzed by Tp′ReO3 [Tp′ = hydrido-tris-(3,5-dimethylpyrazolyl)borate] in benzene at 75-105 °C. The reaction tolerates a wide variety of functional groups including ketones (conjugated or non-conjugated to the new double bond), esters, nitriles, ethers, silyl ethers and phthalimides. Relative rates vary with substitution pattern and electronics; in general, monosubstituted and 2,2-disubstituted epoxides react fastest, and cis-2,3-disubstituted systems react faster than trans. Electron-withdrawing substituents promote the reaction.
- Gable, Kevin P.,Brown, Eric C.
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p. 2243 - 2245
(2007/10/03)
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- Hydrolysis and Alcoholysis of Esters of o-Nitrobenzenesulfonic Acid
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The rate of solvolysis of esters of o-nitrobenzenesulfonic acid with water and C1-C4 alcohols is satisfactorily described by two-parametric Hammett-Taft equation with predominating effect of the electronic factor σ*. The effect of the structure of the hydrocarbon rest in the sulfonic ester group does not fit to this relationship.
- Sendega,Makitra,Pirig
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p. 1438 - 1446
(2007/10/03)
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- THE WITTIG REARRANGEMENT AS A PRACTICAL METHOD FOR ALDEHYDE SYNTHESIS
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If the rearrangement of metalated allyl ethers 2 (or 4) is accomplished in the presence of potassium tert-butoxide, primary alkyl groups preferentially migrate to the unsubstituted allylic terminus (γ-position).Enolates 7 and 1-vinylalcoholates 6 (by alkyl migration to the α-position, adjacent to the oxygen atom) are produced in an approximate ratio of 9 : 1.Because of the endo-configuration of their organometallic precursors, the enolates exclusively emerge in the (Z)-configuration as shown by trapping with chlorotrimethylsilane and isolation of the resulting O-silyl (Z)-enethers.Hydrolysis of the latter affords the corresponding aldehydes with good yields. -The rearrangement is mechanistically still obscure.A concerted process as the main reaction mode is unlikely.The intermediacy of zwitterionic metallomers 18 and solvent caged radical pairs 17 is tentatively suggested.
- Schlosser, Manfred,Strunk, Sven
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p. 2649 - 2664
(2007/10/02)
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- IODINE MEDIATED SYNTHESIS OF ALKYL TERTIO-ALKYL ETHERS
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Mixed alkyl t-alkyl ethers have been prepared by the selective coupling of the alcohol precursors.Dehydration was promoted by iodine under hydrogen pressure at 100 deg C.
- Jenner G.
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p. 2445 - 2448
(2007/10/02)
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- Palladium-Catalyzed Decarboxylation-Carbonylation of Allylic Carbonates To Form β,γ-Unsaturated Esters
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Allyl alkyl carbonates undergo a smooth decarboxylation-carbonylation reaction to afford β,γ-unsaturated esters at 50 deg C under atmospheric or low pressure of carbon monoxide and neutral conditions in the presence of palladium-phosphine complexes as catalysts.The reaction offers a very good method for the preparation of β,γ-unsaturated esters from allylic alcohols.
- Tsuji, Jiro,Sato, Koji,Okumoto, Hiroshi
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p. 1341 - 1344
(2007/10/02)
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- Autoxidation of Allyl Ether Compounds. Part II. Reactivity of Alkyl Allyl Ethers
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The effect of the structure of alkyl allyl ethers on their autoxidation behaviour was investigated by measuring oxygen consumption rates in cobalt catalysed liquid phase oxidations at 30 deg C.The oxidation rates were found to vary considerably depending on the structure of the alkyl group.The rate determining step is intramolecular.The structural effects on the oxidation rates were interpreted as differences in the isomerization rates of peroxy radicals via intramolecular hydrogen transfers.The ease of the hydrogen abstractions were found to decrease in the order of β>γ>α depending on the position of the hydrogen in the alkyl group relative to the etheral oxygen.The contribution of a hydrogen to the autoxidation rate was also found to depend on the nature of the broken C-H bond, decreasing in the order of tert>sec>prim.
- Toivonen, Hannu
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- Production of tetrahydrofuran
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Tetrahydrofuran is produced by converting allyl alcohol to an allyl t-alkyl or -cycloalkyl ether of the general formula: STR1 wherein R1 and R2 each, independently of the other, represent a C1 to C4 alkyl radical, and R3 and R4 each, independently of the other, represent a hydrogen atom or a C1 to C3 alkyl radical, or wherein R1 represents a C1 to C4 alkyl radical, R2 and R3 together with the carbon atoms to which they are attached form a 5-membered or 6-membered cycloaliphatic ring, and R4 represents a hydrogen atom or a C1 to C3 alkyl radical, followed by reacting resulting compound of formula (III) under hydroformylation conditions with carbon monoxide and hydrogen in the presence of a hydroformylation catalyst to form a corresponding aldehyde-ether of the general formula: STR2 reducing resulting aldehyde-ether of the general formula (I) a corresponding hydroxy-ether of the general formula: STR3 and cleaving resulting hydroxy-ether of the general formula (II) under dehydrating conditions to produce tetrahydrofuran. Typically R1 and R2 each represent a methyl group while R3 and R4 each represent a hydrogen atom. The alkene of the general formula: STR4 released upon cleavage of the hydroxy-ether of formula (II) can be recycled for reaction with further allyl alcohol to form a further quantity of the ether of the general formula (III).
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- Production of butyrolactone
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Butyrolactone is produced by oxidizing an aldehyde-ether of the general formula: STR1 wherein R1 and R2 each, independently of the other, represent a C1 to C4 alkyl radical, and R3 and R4 each, independently of the other, represent a hydrogen atom or a C1 to C3 alkyl radical, or wherein R1 represents a C1 to C4 alkyl radical, R2 and R3 together with the carbon atoms to which they are attached form a 5-membered or 6-membered cycloaliphatic ring, and R4 represents a hydrogen atom or a C1 to C3 alkyl radical, to form an acid ether of the general formula: STR2 followed by deetherification, dehydration and cyclization. Oxidation can be carried out with e.g. gaseous oxygen. Deetherification can be accomplished by contact with an acid catalyst, while cyclization may occur spontaneously. A cyclic process is described in which allyl alcohol is converted by reaction with a suitable olefin, e.g. iso-butylene, to an allyl ether of a tertiary alcohol, e.g. allyl t-butyl ether, which is then hydroformylated to form the compound of formula (I), while the olefin, e.g. iso-butylene, released on deetherification of the acid ether of formula (II), is recycled to the allyl ether formation step.
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