- The Baeyer-Villiger oxidation versus aromatic ring hydroxylation: Competing organic peracid oxidation mechanisms explored by multivariate modelling of designed multi-response experiments
-
Peroxy acids can be used as the terminal oxidant for the Baeyer-Villiger oxidation of acetophenones and for direct ring hydroxylation of methoxy-substituted benzenes. An oxidative system involving 3-chloroperbenzoic acid (mCPBA) and 2,6-dimethoxyacetophenone as model substrate was investigated by means of statistical experimental design, multivariate modelling and response surface methodology. The outcome of the organic peracid oxidation experiments was portrayed by a multi-response matrix consisting of the yields of three different compounds; 2,6-dimethoxyphenyl acetate, 1-(4-hydroxy-2,6-dimethoxy-phenyl)ethanone and 3-hydroxy-2,6-dimethoxy-phenyl acetate. The optimized reaction protocol was utilized to investigate a series of various substituted acetophenones. The overall investigation revealed that both the molecular structure of the acetophenone substrate and the experimental conditions exhibited a substantial impact on whether the oxidation reaction follows the oxygen insertion or direct ring hydroxylation mechanism. An improved protocol for the direct ring hydroxylation was also obtained from the experimental and modelling described herein.
- Gambarotti, Cristian,Bj?rsvik, Hans-René
-
p. 619 - 628
(2015/09/28)
-
- Attempts directed towards the synthesis of intermediate (aryne)chromium complexes from aryl triflates and from (haloarene)chromium complexes
-
The generation of (I·6-aryne)chromium complexes as reactive intermediates was investigated in two ways. Although earlier attempts directed towards triflate eliminations from a variety of tricarbonyl(phenyl triflate)chromium complexes had failed, more electron-rich phenyl triflate complexes were considered. This was accomplished either by substitution with two methoxy groups in the arene ligand or by replacement of one of the three carbonyl ligands of the tricarbonylchromium complex with triphenylphosphane. However, the attempted elimination still did not take place; in spite of the increased electron densities in the aromatic ligands, anionic thia-Fries rearrangements were observed in high yields at -78 °C. As an alternative, elimination of lithium fluoride was tested. Tricarbonyl(2-lithiofluorobenzene) chromium(0) was generated by tin/lithium exchange. After hydrolytic workup, tricarbonyl(fluorobenzene)chromium was obtained as the main product, indicating that the lithiation step had been successful. A dimeric side product provided evidence for the intermediacy of (benzyne)tricarbonylchromium. Copyright
- Werner, Georg,Butenschoen, Holger
-
body text
p. 3132 - 3141
(2012/06/30)
-
- Gold(III)-catalyzed direct acetoxylation of arenes with iodobenzene diacetate
-
AuCl3-catalyzed direct acetoxylation of electron-rich aromatic compounds has been achieved with iodobenzene diacetate as the acetoxylation reagent.
- Qiu, Di,Zheng, Zhitong,Mo, Fanyang,Xiao, Qing,Tian, Yu,Zhang, Yan,Wang, Jianbo
-
supporting information; experimental part
p. 4988 - 4991
(2011/11/13)
-
- Electrophilic components in the electrochemical acetoxylation of substituted arenes
-
The mechanism of anodic acetoxylation of substituted arenes under conditions of undivided galvanostatic electrolysis in MeCN containing acetate is suggested and an important role of electrophilic components (AcOH or ZnCl2) catalyzing transformation of intermediate ipso-acetoxylated polysubstituted arenonium cations to corresponding ortho-acetoxylated arenonium cations, which give acetoxylation products after deprotonation, is experimentally proved.
- Burasov, Alexander V.,Petrosyan, Vladimir A.
-
p. 196 - 197
(2008/12/22)
-
- Efficient and green telescoped process to 2-methoxy-3-methyl-[1,4] benzoquinone
-
A telescoped process for the preparation of 2-methoxy-3-methyl-[1,4] benzoquinone is disclosed. When this novel process is compared to the prevailing method that utilizes Na2Cr2O7 as the oxidant, the novel process represen
- Rodriguez Gonzalez, Raquel,Gambarotti, Cristian,Liguori, Lucia,Bjorsvik, Hans-Rene
-
p. 1703 - 1706
(2007/10/03)
-
- Synthesis of methoxy-substituted phenols by peracid oxidation of the aromatic ring
-
A novel benign protocol for the preparation of hydroxy-methoxybenzene derivatives is disclosed. By utilizing this protocol, activated aromatic compounds such as l,3-dimethoxy-2-methyl-benzene and 1-(2,6-dimethoxyphenyl) ethanone are smoothly converted to the corresponding monohydroxylated compound. The reaction can be considered to be a normal aromatic electrophilic substitution reaction, and the regioselectivity for the reaction thus follows the similar rules as for electrophilic substitutions. The protocol is composed by benign reagents, namely, hydogenperoxide, acetic acid, and p-toluene sulfonic acid, which lead to the production of ethaneperoxoic acid in situ. The ethaneperoxoic acid operates as the hydroxylating reagent. The hydroxylation reaction is completed within a short period and requires moreover only mild experimental conditions, which make this novel protocol a green, cheap, and rapid process leading to hydroxy-methoxybenzene derivatives. The proposed reaction mechanism is supported by density functional theory and NMR spectroscopy experiments. The mechanism is constituted by two discrete steps: (a) addition of OH+ to the most nucleophilic carbon atom of the aromatic ring, which is the rate-determining step, and (b) the loss of the proton from the aromatic ring.
- Bjorsvik, Hans-Rene,Occhipinti, Giovanni,Gambarotti, Cristian,Cerasino, Leonardo,Jensen, Vidar R.
-
p. 7290 - 7296
(2007/10/03)
-
- Regularities of anodic acetoxylation of 1,4-dimethoxybenzene in protic and aprotic media
-
Electrochemical acetoxylation of 1,4-dimethoxybenzene during amperostatic electrolysis in an undivided cell at Pt electrodes in MeCN or MeOH solutions containing Et4NOAc gives 2,5-dimethoxyphenyl acetate if AcOH or CH2Cl2 co-solvent has been added in a concentration of ≥50%. The reaction mechanism includes a nucleophilic attack of AcO - ion on the ipso-position of 1,4-dimethoxybenzene radical cation. The process efficiency depends on factors that determine the stability and reactivity of the intermediate 1,4-dimethoxy-1-acetoxyarenonium cation.
- Petrosyan,Vakhotina,Burasov
-
p. 1580 - 1584
(2007/10/03)
-
- Hypervalent iodine-induced nucleophilic substitution of para-substituted phenol ethers. Generation of cation radicals as reactive intermediates
-
A novel hypervalent iodine induced nucleophilic substitution of para-substituted phenol ethers in the presence of a variety of nucleophiles is described. UV and ESR spectroscopic studies indicate that this reaction proceeds via cation radicals, [ArH?+], as reactive intermediates generated by single-electron transfer (SET) from a charge-transfer (CT) complex of phenol ethers with phenyliodine(III) bis(trifluoroacetate) (PIFA). This is the first case that involves a radical intermediate on hypervalent iodine oxidations of aromatic compounds.
- Kita, Yasuyuki,Tohma, Hirofumi,Hatanaka, Kenji,Takada, Takeshi,Fujita, Shigekazu,Mitoh, Shizue,Sakurai, Hiromu,Oka, Shigenori
-
p. 3684 - 3691
(2007/10/02)
-
- Mechanistic Studies of Selective Catechol Formation from o-Methoxyphenols using a Copper(II)-Ascorbic Acid-Dioxygen System
-
Mechanistic details of selective conversion of o-methoxyphenols to the corresponding catechols using a Cu2+-ascorbic acid-O2 system, were studied. 2,5-Dimethoxyphenol was converted predominantly to the o-demethylated compound and partially to the m-demethylated one.Anisole with no phenolic hydroxy group was much less reactive.When guaiacol (1). guaiacol and 2-methoxy-6-methoxyphenol was used as substrates, moderate intermolecular and intramolecular kinetic isotope effects were observed (1.4-1.9). Catechol was derived from 1 in nine-fold excess over catechol when the reaction was run in an 18O2 atmosphere with natural water as a solvent, though no catechol was formed when using natural O2 and H218O.It was determined that the Cu2+-ascorbic acid-O2 system operates in a monooxygenase mode because the oxygen atom of dioxygen (not water) was incorporated into the products, and this oxidative conversion proceeded mainly via ipso-substitution at the methoxy position, probably with hydroxyl radical coordinated to the cupric ion as the active oxygen species.
- Aihara, Kazuhiro,Urano, Yasuteru,Higuchi, Tsunehiko,Hirobe, Masaaki
-
p. 2165 - 2170
(2007/10/02)
-
- Studies of Chromenes. Part 9. Syntheses of Chromenequinones
-
Syntheses of 2,2-dimethylchromene-5,8-quinone, 2,2-dimethylchromene-6,7-quinone, and 6,7-dimethoxy-2,2-dimethylchromene-5,8-quinone are described.Being easily bioreductible to electron-rich chromenes these compounds, and their oxirane derivatives, are of
- Brown, Philip E.,Lewis, Robert A.,Waring, Mark A.
-
p. 2979 - 2988
(2007/10/02)
-
- SELECTIVE DEALKYLATIONS OF ARYL ALKYL ETHERS AND THIOETHERS BY SODIUM IN HMPA
-
The reaction of sodium with bis- and tris(alkoxy)benzenes in HMPA gives selectively the products of monodealkylation.The reaction proceeds through a dianion which fragments into an alkyl and an aryloxy anion.The positional selectivity of this fragmentation is governed by the structure of both the alkyl and aryloxy groups.With bis- and tris(alkoxy)benzenes which for symmetry reasons can afford aryloxy anions having the same basicity, the dealkylation involves exlusively the less substituted alkyl group.On the contrary, in the asymmetric terms, the positional selectivity of the dealkylation process is governed by the basicity of the aryloxy anion.On the basis of these concepts several efficient and synthetically useful reactions have been developed.In most cases the selectivity obtained in the present reactions in different from that observed with other previously developed methods which use sodium methoxide or sodium alkenethiolates in HMPA.It is shown that the appropriate choice of the reagent allows selective dealkylation of the desired alkoxy group of a poly(alkoxy)benzene.The reaction of sodium with bis(alkylthio)benzenes in HMPA gives the bis(mercapto)benzenes.If the reduction is carried out with a solution of sodium in HMPA, the reaction gives instead the products of monodealkylation.This however is not selective.It is suggested that in the case of thioethers the dealkylation products originate from the fragmentation of the radical anions.
- Testaferri, L.,Tiecco, M.,Tingoli, M.,Chianelli, D.,Montanucci, M.
-
p. 3687 - 3692
(2007/10/02)
-
- Phytochemistry of Genus Gentiana. XXVI. Identification of a New Di-O-glucosyl Cinnamoyl-C-glucosylflavone in the Leaves of Gentiana X marcailhouana RY.
-
A new di-O-glucosyl cinnamoyl-C-glucosylflavone has been identified as 4'-O-β-D-glucosyl-2''-O-isoorientin (1).
- Luong, Minh Duc,Saeby, Jan,Fombasso, Pierre,Jacot-Guillarmod, Andre
-
p. 2741 - 2745
(2007/10/02)
-