- Visible light mediated oxidation of benzylic sp3 C-H bonds using catalytic 1,4-hydroquinone, or its biorenewable glucoside, arbutin, as a pre-oxidant
-
Benzylic ethers undergo a visible light induced C-H activation and oxygen insertion to give the corresponding benzoate esters in moderate to good yields. The conditions employ substoichiometric amounts of 1,4-hydroquinone with copper(ii) chloride dihydrate as an electron-transfer mediator, oxygen as the terminal oxidant and dimethyl carbonate as solvent under visible light irradiation. The naturally occurring glucoside, arbutin, which is commercially available or can be accessed via extraction of the leaves of bearberry (Arctostaphylos uva-ursi) or elephant ears (Bergenia crassifolia) can be used as a biorenewable source of 1,4-hydroquinone. The methodology exploits the increase in oxidizing ability of quinones upon irradiation with visible light, and offers a sustainable alternative for the late stage oxidative functionalization of benzylic C-H bonds. It is applicable to a range of cyclic benzylic ethers such as isochromans and phthalans, and simple benzyl alkyl ethers. It can also be applied in the oxidation of benzylic amines into amides, and of diarylmethanes into the corresponding ketones. Mechanistic studies suggest that the reaction proceeds by H-abstraction by the photo-excited triplet benzoquinone to give a benzylic radical that subsequently reacts with molecular oxygen.
- Finney, Laura C.,Mitchell, Lorna J.,Moody, Christopher J.
-
supporting information
p. 2242 - 2249
(2018/05/28)
-
- Iodine-catalyzed transformation of aryl-substituted alcohols under solvent-free and highly concentrated reaction conditions
-
Iodine-catalyzed transformations of alcohols under solvent-free reaction conditions (SFRC) and under highly concentrated reaction conditions (HCRC) in the presence of various solvents were studied in order to gain insight into the behavior of the reaction intermediates under these conditions. Dimerization, dehydration and substitution were the three types of transformations observed with benzylic alcohols. Dimerization and substitution reactions were predominant in the case of primary- and secondary alcohols, whereas dehydration prevailed in the case of tertiary alcohols. The relative reactivity of substituted 1-phenylethanols in I2-catalyzed dimerization under SFRC provided a good Hammett plot ρ+ = -2.8 (r2 = 0.98), suggesting the presence of electron-deficient intermediates with a certain degree of developed charge in the rate-determining step.
- Jereb, Marjan,Vra?i?, Dejan
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p. 747 - 762
(2018/01/17)
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- Sulfated tungstate as hydroxyl group activator for preparation of benzyl, including p-methoxybenzyl ethers of alcohols and phenols
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Sulfated tungstate was found to be an effective heterogeneous and reusable catalyst for hydroxy group activation–mediated preparation of benzylic ethers including p-methoxybenzylic ethers of a wide range of alcohols and phenols under mild reaction conditions.
- Katkar, Kamlesh V.,Veer, Sachin D.,Akamanchi, Krishnacharya G.
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supporting information
p. 1893 - 1901
(2016/11/25)
-
- 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.
- Mochalov,Fedotov,Trofimova,Zefirov
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p. 503 - 512
(2016/06/13)
-
- Cucurbit[7]uril promoting PdCl2-catalyzed cross-coupling reaction of benzyl halides and arylboronic acids in aqueous media
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The research provides a novel approach for producing diarylmethane derivatives using CB[7]-NaCl-PdCl2catalyzed Suzuki cross-coupling reaction of benzyl chloride derivatives and arylboronic acids in ethanol aqueous solution.
- Zhao, Guangkuan,Wang, Zhen,Wang, Ruixin,Li, Jingya,Zou, Dapeng,Wu, Yangjie
-
supporting information
p. 5319 - 5322
(2015/01/16)
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- Proton-exchanged montmorillonite-mediated reactions of methoxybenzyl esters and ethers
-
Proton-exchanged montmorillonite (H-mont) was found to be an eco-friendly and cost-effective catalyst for the generation of O-methylated quinone methides (QM) from the corresponding p or o-methoxybenzyl esters and ethers. Nucleophilic trapping of the O-methylated QM with arenes, alcohols, 1,3-dicarbonyl compounds, silyl enol ethers, and allylsilanes has been carried out, respectively, leading to eco-friendly benzylation reactions. Using this protocol, H-mont-mediated deprotection of PMB-protected esters and ethers have been realized for the first time. This work would pave the way for further exploration in O-alkylated QM that are of chemical and biological significance.
- Chen, Dongyin,Xu, Chang,Deng, Jie,Jiang, Chunhuan,Wen, Xiaoan,Kong, Lingyi,Zhang, Ji,Sun, Hongbin
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p. 1975 - 1983
(2014/03/21)
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- A very practical and selective method for PMB protection of alcohols
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A very simple, practical and efficient one-step heterogeneous protocol for the PMB protection of alcohols using Amberlyst-15 has been developed. The stability and hazard issues regarding PMBCl and PMBBr are totally avoided by directly using anisyl alcohol for the protection. Alcohols are protected in very good yields. The selective mono-PMB protection of diols as well as di-PMB protection of diols was achieved in good yields, along with the demonstration of recyclability of the catalyst.
- Chavan, Subhash P.,Harale, Kishor R.
-
experimental part
p. 4683 - 4686
(2012/09/05)
-
- Direct synthesis of unsymmetrical ethers from alcohols catalyzed by titanium cation-exchanged montmorillonite
-
Titanium-exchanged montmorillonite (Ti4+-mont) was found to act as an efficient heterogeneous catalyst for the etherification of a wide range of alcohols under mild reaction conditions. Ti4+-mont was reusable with retention of high efficiency and applicable to scale-up reaction conditions. The Royal Society of Chemistry 2012.
- Mitsudome, Takato,Matsuno, Tsuyoshi,Sueoka, Shoichiro,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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supporting information; experimental part
p. 610 - 613
(2012/04/23)
-
- New method for the synthesis of benzyl alkyl ethers mediated by FeSO 4
-
The synthesis of benzyl alkyl ethers from benzyl bromides and alcohols using FeSO4 as a recoverable and reusable mediator has been described without use of base and cosolvent under mild conditions.
- Joshi, Girdhar,Adimurthy, Subbarayappa
-
experimental part
p. 720 - 728
(2011/03/22)
-
- A novel, chemoselective and efficient microwave-assisted deprotection of silyl ethers with Selectfluor
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A novel microwave-assisted, chemoselective and efficient method for the cleavage of silyl ethers (aliphatic and aromatic) catalyzed by Selectfluor is reported. A wide range of TBS-, TIPS-, and TBDPS-protected alkyl silyl ethers can be chemoselectively cleaved in high yield in the presence of aryl silyl ethers. The chemoselective deprotection of phenolic TBS ethers, and not the TIPS- or TBDPS-protected phenolic ethers, and the deprotection of silyl esters were also achieved under these reaction conditions. In addition, the transetherification and etherification of benzylic hydroxy groups in alcoholic solvents is observed.
- Shah, Syed Tasadaque A.,Singh, Surendra,Guiry, Patrick J.
-
experimental part
p. 2179 - 2182
(2009/07/01)
-
- Chemoselective etherification of benzyl alcohols using 2,4,6-trichloro-1,3, 5-triazine and methanol or ethanol catalyzed by dimethyl sulfoxide
-
An efficient method for the transformation of benzyl alcohols into their methyl or ethyl ethers has been established using 2,4,6-trichloro-1,3,5-triazine (TCT) and dimethyl sulfoxide in methanol or ethanol. This procedure chemoselectively converts benzylic hydroxys into their methyl or ethyl ethers in the presence of aliphatic or phenolic hydroxys. Georg Thieme Verlag Stuttgart.
- Sun, Lili,Guo, Yuping,Peng, Guisheng,Li, Chunbao
-
experimental part
p. 3487 - 3491
(2009/05/26)
-
- Water compatible gold(III)-catalysed synthesis of unsymmetrical ethers from alcohols
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An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl4, is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols.
- Cuenca, Ana B.,Mancha, Gisela,Asensio, Gregorio,Medio-Simon, Mercedes
-
experimental part
p. 1518 - 1523
(2009/04/04)
-
- A kinetic model for water reactivity (avoiding activities) for hydrolyses in aqueous mixtures - Selectivities for solvolyses of 4-substituted benzyl derivatives in alcohol-water mixtures
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For solvolyses of various benzyl substrates in ethanol-water (EW) and methanol-water (MW) mixtures, product selectivities (S) are reported for chlorides at 75°C defined as follows using molar concentrations: S= ([ether product]/[alcohol product]) × ([water]/[alcohol solvent]). The results support earlier evidence that solvolyses of 4-nitrobenzyl substrates are S N2 processes, which are not susceptible to mechanistic changes over the whole range of solvents from water to alcohol. S values at 25 and/or 45°C in EW and MW, and additional kinetic data including kinetic solvent isotope effects (KSIE) are reported for solvolyses of 4-nitrobenzyl mesylate and tosylate. A kinetic model, explaining both rates and product, is proposed; a general medium effect due to solvent polarity is combined in one parameter with solvent effects on the nucleophilicity of the water and alcohol molecules acting as nucleophiles in SN2 reactions. According to this model, as alcohol is added to water the rate of reaction decreases due to a decrease in solvent polarity, but the nucleophilicity of water increases relative to alcohol. The availability of experimental rate and product data over the whole range of solvent compositions from alcohol to water, reveals limitations of alternative approaches using activities. Copyright
- Bentley, T. William,Koo, In Sun,Choi, Hojune,Llewellyn, Gareth
-
p. 251 - 256
(2008/09/20)
-
- Iodine catalyzed selective O-alkylation of alcohols with orthoesters
-
In the present communication O-alkylation of a number of allylic and benzylic alcohols has been described.
- Kumar,Anjaneyulu,Joyasawal, Sipak,Pawan Chakravarthy,Naveen Kumar,Yadav
-
p. 189 - 192
(2008/02/13)
-
- Oxidation of benzylsilanes and benzyltins by oxovanadium(V) compound and molecular oxygen
-
Benzylsilane and benzyltin compounds were oxidized by oxovanadium(V) compound under an oxygen atmosphere to afford the corresponding aromatic aldehydes (ketones) and/or carboxylic acids. In the reaction of benzyltins, oxovanadium(V) compound can be reduce
- Hirao, Toshikazu,Morimoto, Chihiro,Takada, Takashi,Sakurai, Hidehiro
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p. 5073 - 5079
(2007/10/03)
-
- Reductive etherification of aromatic aldehydes with decaborane
-
Aromatic aldehydes were easily convened to the corresponding ethers in methanol or ethanol using decaborane at r.t. under nitrogen in high yields.
- Lee, Seung Hwan,Park, Yong June,Yoon, Cheol Min
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p. 6049 - 6050
(2007/10/03)
-
- Synthesis and reactivity of 5,8-dihydroxythioflavanone derivatives
-
The synthesis of substituted chalcones, thioflavanones, and thioflavones hydroxylated in both A and B rings is described. Acetoquinone (1) was transformed into 2,5-dihydroxy-6-(p-methoxybenzylmercapto)acetophenone (2) and subsequently into its 2,5-dimethoxy (3) and 2,5-dibenzyloxy (4) derivatives. Compounds 3 and 4 were condensed with suitable benzaldehydes to give chalcones 5-10. The thiol group of the chalcones was deprotected by a cleavage of the p-methoxybenzyl protecting group using a new, mild method (silver nitrate in boiling ethanol, 2 h), and the products were cyclized to thioflavanones (15-20). Dehydrogenation of the thioflavanones gave related thioflavones (25-27). Deprotection of methoxy and benzyloxy groups is also described.
- Konieczny, Marek T.,Horowska, Barbara,Kunikowski, Antoni,Konopa, Jerzy,Wierzba, Konstanty,Yamada, Yuji,Asao, Tetsuji
-
p. 359 - 364
(2007/10/03)
-
- Stereospecific Synthesis of β-D-Fructofuranosides Using Thioglycoside Donors and Internal Aglycon Delivery
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Stereospecific synthesis of β-D-fructofuranosides has been accomplished by the application of an internal acceptor delivery approach. The acceptor, ethanol or monosaccharides, is initially tethered to the fructofuranose 3-hydroxyl group, adjacent to the anomeric center and on the β-side of the furanose ring, as part of a mixed p-methoxybenzaldehyde acetal, which is formed by DDQ-oxidation of ethyl 1,4,6-tri-O-benzyl-3-O-(4-methoxybenzyl)-2-thio-D-fructofuranoside in the presence of the acceptor or of the p-methoxybenzylated acceptor in the presence of the corresponding 3-OH fructofuranoside. Then, activation of the thioglycoside with a thiophilic promoter allows the delivery of the acceptor from the acetal to the activated anomeric center to yield the β-linked fructofuranoside in high yields (76-85%). If promoters with nonnucleophilic anions (triflate, perchlorate) are used, the intermediate acetal decomposes to produce the β-fructofuranoside products as 3-OH derivatives. However, if NIS is used as promoter, the N-succinimide anion interacts with the benzylidene carbon to give the β-fructofuranoside products as mixed fructofuranoside-3-O-yl N-succinimide p-methoxybenzaldehyde acetals.
- Krog-Jensen, Christian,Oscarson, Stefan
-
p. 1780 - 1784
(2007/10/03)
-
- Solvolytic Reactions in Fluorinated Alcohols. Role of Nucleophilic and Other Solvation Effects
-
Rate constants and products for solvolyses of chlorodiphenylmethane (Ph2CHCl) and p-methoxybenzyl chloride in 2,2,2-trifluoroethanol (TFE)/water and TFE/ethanol are reported, along with additional kinetic data for solvolyses of tert-butyl and other alkyl halides (RX) in 97% w/w TFE/water and in 97% w/w hexafluoropropan-2-ol/water (HFIP). Results are discussed in terms of the solvent ionizing power (Y) and the solvent nucleophilicity (N), and contributions from other solvation effects are considered. Comparisons with other SN1 solvolyses show that solvolyses of Ph2CHCl in TFE mixtures are unexpectedly fast, but product ratios are unexceptional. An additional solvation effect influences solvolyses leading to delocalized cations, and a delocalized cationic transition state for concerted elimination may explain the recent results of Takeuchi et al., (J. Org. Chem. 1997, 62, 4904) without the need to postulate additional specific solvation effects for adamantyl systems, such as Bronsted-base solvation of α- and β-hydrogen atoms; concerted elimination may occur because simple tertiary alkyl cations are too unstable to form in predominantly aqueous media. Iodide/bromide and bromide/chloride rate ratios are very similar for 1-adamantyl halides and corresponding solvolyses of tert-butyl halides; these ratios decrease in the order aq EtOH > TFE > HFIP, as expected for an electrophilic solvation effect (this effect can readily be incorporated into Y values). From kinetic data for a series of tertiary alkyl chlorides in 97% TFE/water, it is shown that the susceptibility of rates of solvolyses of RCl to N decreases with an increase in steric hindrance or with an increase in charge stabilization. Also, the small kinetic solvent isotope effects for typical solvolyses (e.g., methyl tosylate) indicate that nucleophilic attack lags behind heterolysis of the C-X bond.
- Bentley, T. William,Llewellyn, Gareth,Ryu, Zoon Ha
-
p. 4654 - 4659
(2007/10/03)
-
- Selective Cross Coupling via Oxovanadium(V)-Induced Oxidative Desilylation of Benzylic Silanes
-
Benzylic silanes bearing an electron-donating group at the ortho- or para-position underwent the oxovanadium(V)-induced one-electron oxidative desilylation due to low ionization potential, which was applied to the intermolecular regioselective coupling with allylic silanes or silyl enol ether.
- Hirao, Toshikazu,Fujii, Takashi,Ohshiro, Yoshiki
-
p. 8005 - 8008
(2007/10/02)
-
- A Relationship between Selectivity and Solvent Composition for Nucleophilic Attack on Carbocations in Alcohol-Water Mixtures
-
Rate constants and products of solvolyses of p-methoxybenzyl chloride 1, chlorodiphenylmethane 2 (Y = Z = H), chloro(4-chlorophenyl)phenylmethane 2 (Y = H, Z= Cl) and chlorobis(4-chlorophenyl)methane 2 (Y = Z = Cl) are reported in ethanol- and methanol-water mixtures at 25 deg C.Product selectivities (S), defined by: S = / are related to four rate constants for reactions involving one molecule of solvent as nucleophile and another molecule of solvent as general base catalyst (e.g. kwa involves water as nucleophile and alcohol as general base, and kww, kaw and kaa are defined similarly).A linear relationship between 1/S and molar ratios of solvent 1/S = (kwa/kaw)(/) + kww/kaw is derived theoretically and validated experimentally for solvolyses of the above substrates from water up to 70percent alcohol-water-in this range of solvents, the contribution from kaa can be neglected.For solvolyses of p-methoxybenzyl chloride, S is independent of pH between pH 2 and 12, S decreases when acetone is added but increases if acetonitrile is added and for 90percent ethanol-water S increases with added LiCl and LiClO4 and increases further if acetonitrile is also present.
- Bentley, T. William,Ryu, Zoon Ha
-
p. 761 - 768
(2007/10/02)
-
- Triazene Drug Metabolites. Part 10. Metal-ion Catalysed Decomposition of Monoalkyltriazenes in Ethanol Solutions
-
The metal ions Fe(2+), Zn(2+) and Cu(2+) bring about the rapid decomposition of 1-aryl-3-alkyltriazenes to the corresponding anilines.For Fe(2+), a linear dependence of the pseudo-first-order rate constant, k0, on was observed, while for Zn(2+) and Cu(2+) plots of k0 versus were curved and indicative of complex formation.For Fe(2+), second-order rate constants k2Fe(2+) for substituted 1-aryl-3-methyltriazenes follow a Hammett relationship giving rise to a ρ value of -3.0.For Zn(2+) and Cu(2+), the data were analysed in terms of an equilibrium konstant, KM(2+), for the dissociation of a metal-ion-triazene complex and the first-order rate constant, for the collapse of this complex to products, k2M(2+).Hammett ρ values of 1.0 for both KZn(2+) and KCu(2+) are found, and the corresponding ρ values for k2Zn(2+) and k2Cu(2+) are -1.3 and -1.9.There is reasonable correlation between the Taft Eg parameter for the alkyl group and KCu(2+), giving a δ value of -1.6.The dependence of k2Cu(2+) on the alkyl group is not simple: k2Cu(2+) decreases in the order Pr > Et * PhCH2 ca. 4-MeOC6H4CH2 > CD3 ca.Me.The reactions catalysed by Cu(2+) are inhibited by added nucleophiles e.g.Br(1-) and N-methylimidazole. A mechanism is proposed in which the triazene complexes to the metal ion via the N(1) nitrogen atom of the E-cis conformer, then undergoes a fast proton transfer to form a complex involving the unconjugated tautomer which subsequently decomposes via unimolecular scission of the N(2)-N(3) bond to form an alkyldiazonium ion and an aniline-metal complex.The observed products then arise from rapid solvolysis of the metal-aniline complex and the alkyl diazonium ion.
- Iley, Jim,Moreira, Rui,Rosa, Eduarda
-
-
- Distinguishing between Solvation Effects and Mechanistic Changes. Effects Due to Differences in Solvation of Aromatic Rings and Alkyl Groups
-
Solvolytic rate constants at 25 deg C are reported for p-methoxybenzylchloride (1) in aqueous binary mixtures with acetone, acetonitrile, dioxane, dimethyl sulfoxide, ethanol, methanol, and 2,2,2-trifluoroethanol and for benzoyl chloride and p-methoxybenzoyl chloride (2) in aqueous acetonitrile and aqueous dioxane.Product selectivities are reported for solvolyses of 1 in aqueous ethanol and methanol.Logarithms of rate constants for solvolyses of 2 correlate linearly with solvolyses of 1 (unit slope and only a small "dispersion" - the tendency for the various binary mix tures to show seperate correlations), showing that the solvation requirements of SN1 reactions of aromatic carboxylic acid chlorides are very similar to those of benzylic chlorides.Similar good correlations are reported vs solvolyses of α-phenylethyl chloride and vs Z values.For SN1 reactions of chlorides in binary mixtures having similar electrophilicities, the phenomenon of dispersion in Grunwald-Winstein plots (vs Y) and the poor correlation vs YCl (reported previously) appears to be due to the differences in solvation between aromatic rings and alkyl groups; this difference is largest for binary aqueous mixtures with methanol > ethanol > aprotic solvents.The complex rate-rate profile for similar solvolytic reactions of benzoyl chloride is dissected quantitatively into contributions from two competing reaction channels, one of which shows only a small "dispersion" in a correlation with solvolyses of 2; these results are consistent with a mainly dissociative reaction channel for solvolyses of benzoyl chloride in highly aqueous media.
- Bentley, T. William,Koo, In Sun,Norman, Simon J.
-
p. 1604 - 1609
(2007/10/02)
-
- Al-NiCl(2°)6H2O-THF: A new, mild and neutral system for selective reduction of organic functional groups
-
A mild and neutral reducing system consisting of Al-NiCl(2°)6H2O-THF has been developed and reacted with a series of organic compounds containing different functional groups in order to evaluate its synthetic utility. It was observed that this system very efficiently reduces the α-enones to the saturated ketones, aromatic aldehydes and ketones to the corresponding alcohols, nitriles and nitroarenes to amines, acid anhydrides and acid chlorides to aldehydes, disulphides to thiols and epoxides to the corresponding alcohols. On the other hand isolated double bonds, carboxylic acids, esters, lactones, primary, benzyl and allyl halides, aliphatic aldehydes and ketones and aliphatic nitro compounds were found to remain inert to this system. Furthermore, the reducing properties of Al-NiCl(2°)6H2O in several other organic solvents were also studied.
- Sarmah,Barua
-
p. 8587 - 8600
(2007/10/02)
-
- Photochemistry of phosphate esters: An efficient method for the generation of electrophiles
-
The photochemical cleavage of benzyl diethyl phosphates, 1a-g, has been examined in tert-butyl alcohol, which produces the corresponding benzyl tert-butyl ether as the major solvolysis product upon direct irradiation. The multiplicity of the reactive excited state has been established as the singlet state. Evidence favoring an intermediate benzyl cation-phosphate ion pair formed from photofragmentation includes oxygen-18 scrambling, racemization of chiral benzyl phosphates, and substituent effects on the rate of reaction. The existence of an electrophilic intermediate is further supported by a linear free energy relationship for the rate of disappearance of 1, kdis, with Hammett σ, which gave a ρ value of -0.90 and for the rate of appearance of 2, kapp, a Hammett ρ value of -0.97. Possible mechanisms including an electron transfer either before or after homolysis or simple heterolysis of the ester bond are evaluated.
- Givens, Richard S.,Matuszewski, Bogdan,Athey, Phillip S.,Robert Stoner
-
p. 6016 - 6021
(2007/10/02)
-
- QUELQUES ASPECTS DE LA REACTIVITE DE L'α-CHLORO α-ETHOXYMETHYLTRIBUTYLETAIN: ETHERIFICATION REDUCTRICE DES ALDEHYDES AROMATIQUES ET MISE EN EVIDENCE DE FORMYLTRIBUTYLETAIN LORS DE LA REACTION D'HYDROLYSE
-
α-Chloro-α-ethoxymethyltributyltin reacts with aromatic aldehydes and leads to benzyl ethyl ethers with formation of tributyltin chloride and carbon monoxide.Analogously the formation of ethoxymethyltributyltin and tributyltyn chloride on hydrolysis of this new organometallic reagent is explained by a process involving formyltributyltin as an unstable intermediate.This explanation is supported by the observation of an electronic spectrum between 350 and 450 nm during the hydrolysis.
- Quintard, Jean-Paul,Elissondo, Bernard,Mouko-Mpegna, David
-
p. 175 - 188
(2007/10/02)
-
- Sulphur-oxygen versus carbon-oxygen bond fission in the solvolysis of benzyl sulphenates
-
In contrast to p-anisyl trichloromethanesulphenate 1, which readily undergoes ethanolysis at room temperature with carbon-oxygen bond fission, the ethanolysis of the corresponding 2-nitrobenzenesulphenate 2 proceeds at a similar rate only at 100°, and involves sulphur-oxygen bond cleavage. While the solvolysis of 1 showed first-order kinetics, the solvolysis of 2 was second-order (first-order with respect to ester and to added base). The solvolysis rate of 2 decreases on going from 100% to 80% ethanol and by using pyridine instead of acetate as base, consistent with an SN2 type mechanism involving nucleophilic displacement at sulphur by the base or lyate ion. The rate of solvolysis of 1 is greatly enhanced in polar solvents and correlates satisfactorily with the ionization of p-methoxyneophyl tosylate. An ionization mechanism to some ion pair species is suggested for the solvolysis of 1.
- Braverman,Reisman
-
p. 3891 - 3896
(2007/10/05)
-