- Regiodivergent oxidation of alkoxyarenes by hypervalent iodine/oxone system
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We have found that the combination of Oxone with an organoiodine compound, i.e., 2-iodobenzoic acid (2-IB), selectively yields p-quinones from monomethoxyarenes under mild conditions. In this reaction system, an organoiodine compound is immediately oxidized by Oxone to generate cyclic hypervalent iodine (III) species in situ, which serves as the specific mediator for the selective p-quinone synthesis, preventing o-quinone formation.
- China, Hideyasu,Tanihara, Kokoro,Sasa, Hirotaka,Kikushima, Kotaro,Dohi, Toshifumi
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- Lewis Acid-Directed Reactions of Quinones with Styrenyl Systems: The Case of 2-Methoxy-3-methyl-1,4-benzoquinone
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Reactions of 2-methoxy-3-methyl-1,4-benzoquinone with various (E)-1-propenylbenzenes promoted by 1 equiv of Ti(IV), as a 1:1 mixture of TiCl4-Ti(O-i-Pr)4, produce rel-(1S,6R,7R,8R)-8-aryl-4,7-dimethyl-3-methoxybicyclo[4.2.0]oct-3-ene-2,5- diones 3 and trans-2-aryl-3,7-dimethyl-6-methoxy-2,3-dihydro-5-benzofuranols 5 as the major products. Reactions promoted by 2 equiv of Ti(IV) as a 1:1 mixture of TiCl4-Ti(O-i-Pr)4 or 1 equiv of either TiCl4, SnCl4, or BF3·OEt2 give regioisomeric rel-(1R,6S,7A,8R)-7-aryl-4,8-dimethyl-3-methoxybicyclo[4.2.0]oct-3-ene-2,5- diones (4) and/or trans-2-aryl-3,6-dimethyl-7-methoxy-2,3-dihydro-5-benzofuranols (6). A mechanism involving regioselective coordination of the various Lewis acids to the quinone is used to explain the formation of the products. These reactions demonstrate the effective regiocontrol exerted over the reactions by the nature of the Lewis acid promoters. Cyclobutanes 3 and 4 cleanly undergo rearrangement to the corresponding benzofuranols 5 and 6 on treatment with protic acid. In contrast, reactions of 2-methoxy-1,4-benzoquinone promoted by either BF3·OEt2 or Ti(IV), as 1 equiv or excess amounts of TiCl4 or 1:1 TiCl4-Ti(O-i-Pr)4, all afford the same regioisomeric products, i.e., rel-(1S,6R,7R,8R)-8-aryl-7-methyl-3-methoxybicyclo[4.2.0]oct-3-ene-2,5-dione 25 and/or trans-2-aryl-3-methyl-6-meth-oxy-2,3-dihydro-5-benzofuranol 27.
- Engler, Thomas A.,Iyengar, Rajesh
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- Combined C-H activation/cope rearrangement as a strategic reaction in organic synthesis: Total synthesis of (-)-colombiasin A and (-)-elisapterosin B
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The total synthesis of (-)-colombiasin A (2) and (-)-elisapterosin B (3) has been achieved. The key step is a C-H functionalization process, the combined C-H activation/Cope rearrangement, between methyl (E)-2-diazo-3-pentenoate and 1-methyl-1,2-dihydrona
- Davies, Huw M. L.,Dai, Xing,Long, Matthew S.
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- Laccase-mediated synthesis of 2-methoxy-3-methyl-5-(alkylamino)- and 3-methyl-2,5-bis(alkylamino)-[1,4]-benzoquinones
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The synthesis of 5-alkylamino- and 2,5-bis(alkylamino)-[1,4]-benzoquinones, showing structural similarity to natural mitomycins, was performed through coupling of 2-methoxy-3-methylhydroquinone with primary amines such as n-octylamine, geranylamine and cy
- Herter, Susanne,Michalik, Dirk,Mikolasch, Annett,Schmidt, Marlen,Wohlgemuth, Roland,Bornscheuer, Uwe,Schauer, Frieder
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- Efficient and green telescoped process to 2-methoxy-3-methyl-[1,4] benzoquinone
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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
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p. 1703 - 1706
(2007/10/03)
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- Access to orthogonal protected phenols - Synthesis of a silylated quinol
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Herein we describe the synthesis of t-butyldimethylsilyl protected quinol (9), using an oxidation/reduction sequence to create the desired orthogonality. The title compound acts as a synthetic equivalent for a quinone, required in the total synthesis of E
- Siddiqi, Shahzad A.,Heckrodt, Thilo J.
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p. 328 - 331
(2007/10/03)
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- Total synthesis of elisabethin A: Intramolecular Diels-Alder reaction under biomimetic conditions
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We describe the first total synthesis of the marine diterpenoid elisabethin A. The synthesis uses (S)-hydroxy-2-methyl-propionate as the chiral starting material, which is elaborated into a dienyl-iodide and added to an aryl acetic acid ester via enolate
- Heckrodt, Thilo J.,Mulzer, Johann
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p. 4680 - 4681
(2007/10/03)
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- Indoloquinones, part 7. Total synthesis of the potent lipid peroxidation inhibitor carbazoquinocin C by an intramolecular palladium-catalyzed oxidative coupling of an anilino-1,4-benzoquinone
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A highly efficient total synthesis of the potent lipid peroxidation inhibitor carbazoquinocin C is presented. The key-step is a palladium(II)-catalyzed oxidative cyclization of an anilino-1,4-benzoquinone to a carbazole-1,4-quinone which proceeds in up to 91% yield. Using this approach the natural product is obtained in four steps and 39% overall yield starting from aniline.
- Kn?lker, Hans-Joachim,Fr?hner, Wolfgang,Reddy, Kethiri R.
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p. 557 - 564
(2007/10/03)
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- Palladium-catalyzed total synthesis of the antibiotic carbazole alkaloids carbazomycin G and H
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A highly efficient palladium-catalyzed synthesis affords carbazole-1,4-quinones which can be transformed directly into the carbazomycins G and H and are shown to represent precursors for several other biologically active carbazole alkaloids.
- Knoelker, Hans-Joachim,Froehner, Wolfgang
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p. 173 - 175
(2007/10/03)
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- Ultrasound-promoted synthesis of substituted phenanthrene-1,4-quinones; the structure of plectranthon D
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A series of tanshinone-type diterpenoids was prepared by ultrasound-promoted and Lewis acid catalyzed, highly regioselective cycloadditions of styrenes with substituted 1,4-benzoquinones as the key step.
- Zhang, Zhao-Rong,Flachsmann, Felix,Moghaddam, Firouz Matloubi,Rueedi, Peter
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p. 2153 - 2156
(2007/10/02)
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- Reactive dyestuffs
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Triphendioxazine reactive dyestuffs of the general formula STR1 with the substituent definition given in the description, are outstandingly suitable for dyeing and printing materials containing hydroxyl groups or amide groups. They give red dyeings with high wet- and light-fastnesses.
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- Oxidation of Methoxy- and/or Methyl-Substituted Benzenes and Naphthalenes to Quinones and Phenols by H2O2 in HCOOH
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The oxidation of a number of arenes (methoxybenzenes, methylbenzenes, and naphthalenes) to quinones and phenols by H2O2 in HCOOH has been examined.Methoxybenzenes were much more easily oxidized to p-benzoquinones than methylbenzenes (e.g., 1,3,5-trimethoxybenzene was oxidized to 2,6-dimethoxy-p-benzoquinone in a 75percent yield and 1,2,4-trimethylbenzene to 2,3,5-trimethyl-p-benzoquinone in a 16percent yield).Electron-withdrawing substituents, such as nitro, cyano, and chloro groups, lowered the conversion of reactants and changed the product selectivity from quinones to phenols.Methoxybenzonitriles were oxidized to corresponding phenols in a moder ate yield (e.g., 2,6-dimethoxybenzonitrile to 3-hydroxy-2,6-dimethoxybenzonitrile in a 39percent yield and a 64percent selectivity).
- Orita, Hideo,Shimizu, Masao,Hayakawa, Takashi,Takehira, Katsuomi
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p. 1652 - 1657
(2007/10/02)
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- Metalation of Phenols. Synthesis of Benzoquinones by the Oxidative Degradation Approach
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In a effort to explore the potential of so-called oxidative degradation approach for the synthesis of quinones, we have investigated the direct metalation of a number of simple phenols such as o- and p-hydroxybenzyl alcohols, benzyl methyl ethers and N,N-dimethylbenzylamines.Apparently, only those phenolic substrates having available both a coordinating group for chelation and an electron-withdrawing group in a 1,3-relationship are efficiently lithiated, by the action of n-BuLi, in a regioselective manner.Those positions on the aromatic nucleus just flanked by a coordinating, or an acid-base, group could be metalated by action of the t-BuLi/THP system, in favorable cases.
- Saa, Jose M.,Llobera, Antonia,Garcia-Raso, Angel,Costa, Antonio,Deya, Pedro M.
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p. 4263 - 4273
(2007/10/02)
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- A NOVEL DEGRADATIVE STRATEGY FOR THE SYNTHESIS OF p-QUINONES.
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p-Hydroxybenzylalcohols undergo Fremy's salt promoted degradative oxidation to give the corresponding p-benzoquinones.A novel strategy for the synthesis of p-benzoquinones based on the regioselective metalation of 2-methoxy-4-methoxymethyl phenols is presented.
- Saa, Jose M.,Morey, Jeronimo,Costa, Antonio
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p. 5125 - 5128
(2007/10/02)
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- Triphendioxazine dyestuffs
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Triphendioxazine dyestuffs of the formula STR1 having the substituent meanings specified in the descriptive part, are highly suitable for dyeing and printing hydroxyl- or amido-containing materials, in particular fibre materials, and produce wash-fast dyeings and prints.
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- CYCLOADDITIONS OF NON-STABILIZED AZOMETHINE YLIDES AND QUINONES SYNTHESIS OF THE RENIERA ISOINDOLE
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Azomethyne ylides, generated from cyanomethylamino silanes and excess silver fluoride, undergo cycloaddition with quinones to give, after oxidation in situ, quinonoid isoindoles.This reaction provides the key step for a short, high yield synthesis of the
- Parker, Kathlyn A.,Cohen, Isaac D.,Padwa, Albert,Dent, William
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p. 4917 - 4920
(2007/10/02)
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- Amine Addition to Unsymmetrical Benzoquinones
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New routes to 2-methoxy-3-methyl-1,4-benzoquinone and 4-methoxy-3-methyl-1,2-benzoquinone have been developed.Both quinones undergo highly regioselective oxidative amination with pyrrolidine and copper acetate, yielding aminoquinones related to the mitomy
- Luly, Jay R.,Rapoport, Henry
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p. 2745 - 2752
(2007/10/02)
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