- En Route to D-Ring Inverted Phorbol Esters
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Phorbol esters are long regarded as tumor promotors, due to protein kinase C (PKC) activation, but more recently higher oxidized natural derivatives have been shown to display antitumor activity. Given the synthetic difficulty, systematic non-natural syst
- Chow, Sharon,Krainz, Tanja,Bernhardt, Paul V.,Williams, Craig M.
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- Hollow, mesoporous, eutectic Zn1?xMgxO nano-spheres as solid acid-base catalysts for the highly regio-selectiveO-methylation of 1,2-diphenols
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The highly regio-selectiveO-methylation of catechol with dimethyl carbonate (DMC), catalyzed by a solid acid-base catalyst, is an environmentally friendly chemical process for industrial production of guaiacol. However, a guaiacol yield below 84% and high reaction temperature above 280 °C limit its industrial application. Here, hollow, mesoporous Zn1?xMgxO nano-spheres with a eutectic structure, denoted as Zn1?xMgxO HMNSs (x= 0.012-0.089), are facilely fabricatedviathe calcination of Mg2+/Zn2+ion-adsorbing carbon spheres at 500 °C in air. In theO-methylation of catechol with DMC at 180 °C, Zn1?xMgxO HMNSs (x= 0.052) afford guaiacol in 95.5% yield with a complete catechol conversion. Furthermore, 89.0-95.3% mono-ether yields with high 1,2-diphenol conversions (94.5-100%) are also obtained for the other 1,2-diphenols bearing -CH3and -Br groups. Moreover, a plausible mechanism for highly selectiveO-methylation of catechol with DMC is proposed, in which the single-site activation and double-site activation of phenolic hydroxyls by the basic oxygen of Mg-O afford guaiacol and veratrole, respectively.
- Liu, Jie,Ma, Xuebing,Wang, Xuri,Xie, Guangxin,Yin, Zuyong,Zhang, Jianing
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p. 7454 - 7466
(2021/11/23)
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- Preparation method of 5-methyl vanillin
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The invention relates to a preparation method of 5-methyl vanillin, which comprises the following steps: 1) by using ortho vanillin as a raw material, carrying out hydrogenation reduction reaction under the action of a hydrogenation catalyst to obtain 6-m
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Paragraph 0017; 0035-0038; 0039-0040; 0041-0042; 0043-0050
(2020/12/30)
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- Biomimetic Design of a 3 D Transition Metal/Carbon Dyad for the One-Step Hydrodeoxygenation of Vanillin
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Enzyme catalysts always show an excellent catalytic selectivity, which is important in biochemistry, especially in catalytic synthesis and biopharming. This selectivity is achieved by combining the binding effect induced by the electrostatic effect of the enzyme to attract a specific substrate and then the prearrangement of the substrates inside the enzyme pocket. Herein, we report a proof-of-concept application of an interfacial electrostatic field induced by constructing Schottky heterojunctions to mimic the electrostatic catalysis of an enzyme. In combination with the 3 D structure, a transition metal/carbon dyad was designed by nanoconfinement methods to promote the differential binding effect and the space-induced organization of the reaction intermediate (vanillyl alcohol) to develop a new one-step hydrogenolysis of vanillin for the production of 2-methoxy-4-methylphenol with a remarkably high selectivity (>99 %).
- Chen, Jie-Sheng,Li, Xin-Hao,Su, Juan,Wang, Hong-Hui,Zhang, Jun-Jun,Zhao, Tian-Jian
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- Atomically Dispersed Co Catalyst for Efficient Hydrodeoxygenation of Lignin-Derived Species and Hydrogenation of Nitroaromatics
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Single-atom catalysts (SACs) have attracted much attention due to their outstanding catalytic performance in heterogeneous catalysis. Here, we report a template sacrificial method to fabricate an atomically dispersed Co catalyst; three kinds of silica templates with different microstructures (MCM-41, SBA-15, and FDU-12) were employed and the effect of pore structure of the templates on the dispersity of Co was investigated. The catalysts fabricated with different templates presented different Co dispersities, leading to distinguishing catalytic performance. The optimized Co1?NC-(SBA) catalyst with atomically dispersed Co displayed outstanding catalytic activity for the hydrodeoxygenation (HDO) of lignin-derived species as well as the hydrogenation of various nitroaromatics. The reaction mechanism of the HDO of vanillin was investigated by using density functional theory calculations as well.
- Du, Congcong,Gao, Shutao,Gao, Yongjun,Huang, Jianyu,Meng, Tao,Qiao, Yuqing,Shang, Ningzhao,Shen, Tongde,Wang, Chun,Wang, Haijun,Wang, Junmin,Wang, Zhi,Wu, Qiuhua,Zhang, Longkang
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p. 8672 - 8682
(2020/09/18)
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- Structural features and antioxidant activities of Chinese quince (Chaenomeles sinensis) fruits lignin during auto-catalyzed ethanol organosolv pretreatment
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Chinese quince fruits (Chaenomeles sinensis) have an abundance of lignins with antioxidant activities. To facilitate the utilization of Chinese quince fruits, lignin was isolated from it by auto-catalyzed ethanol organosolv pretreatment. The effects of three processing conditions (temperature, time, and ethanol concentration) on yield, structural features and antioxidant activities of the auto-catalyzed ethanol organosolv lignin samples were assessed individually. Results showed the pretreatment temperature was the most significant factor; it affected the molecular weight, S/G ratio, number of β-O-4′ linkages, thermal stability, and antioxidant activities of lignin samples. According to the GPC analyses, the molecular weight of lignin samples had a negative correlation with pretreatment temperature. 2D-HSQC NMR and Py-GC/MS results revealed that the S/G ratios of lignin samples increased with temperature, while total phenolic hydroxyl content of lignin samples decreased. The structural characterization clearly indicated that the various pretreatment conditions affected the structures of organosolv lignin, which further resulted in differences in the antioxidant activities of the lignin samples. These results can be helpful for controlling and optimizing delignification during auto-catalyzed ethanol organosolv pretreatment, and they provide theoretical support for the potential applications of Chinese quince fruits lignin as a natural antioxidant in the food industry.
- Cheng, Xi-Chuang,Guo, Xin-Ran,Liu, Hua-Min,Liu, Yu-Lan,Qin, Zhao,Wang, Xue-De
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p. 4348 - 4358
(2020/09/22)
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- Deoxyalkylation of guaiacol using haggite structured V4O6(OH)4
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When V2O5 is used for the deoxygenation of guaiacol in methanol, it is reduced in situ to haggite structured V4O6(OH)4. Guaiacol prevents further reduction of the haggite phase in methanol and haggite catalyzes the partial deoxygenation of guaiacol. Haggite is a metastable redox catalyst for the deoxygenation of guaiacol, which follows the reverse Mars-van Krevelen mechanism. In addition, haggite is also a Lewis acid catalyst and catalyzes the alkylation of guaiacol with methanol as the alkylation reagent. The main products of the guaiacol deoxyalkylation are 2,6-dimethylphenol, 2-methoxy-6-methylphenol, 2,4,6-trimethylphenol, 2,3,6-trimethylphenol, 2,3,5,6-tetramethylphenol and 6-methyl-2-tert-butylphenol. Oligomerization takes place during the reaction but it is reversible. When the reaction is performed at 300 °C for 6 h, the 83.5% total selectivity for alkylphenols is achieved with a 99.0% conversion.
- Yan, Fei,Wen, Zhe,Wu, Kai,Cui, Kai,Mai, Fuhang,Ma, Zewei,Sang, Yushuai,Bai, Yunfei,Chen, Hong,Li, Yongdan
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p. 1922 - 1932
(2019/04/29)
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- Examination of Selectivity in the Oxidation of ortho- and meta-Disubstituted Benzenes by CYP102A1 (P450 Bm3) Variants
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Cytochrome P450 CYP102A1 (P450 Bm3) variants were used to investigate the products arising from the P450 catalysed oxidation of a range of disubstituted benzenes. The variants used all generated increased levels of metabolites compared to the wild-type enzyme. With ortho-halotoluenes up to six different metabolites could be identified whereas the oxidation of 2-methoxytoluene generated only two aromatic oxidation products. Addition of an ethyl group markedly shifted the selectivity for oxidation to the more reactive benzylic position. Epoxidation of an alkene was also preferred to aromatic oxidation in 2-methylstyrene. Significant minor products arising from the migration of one substituent to a different position on the benzene ring were formed during certain P450-catalysed substrate turnovers. For example, 2-bromo-6-methylphenol was formed from the turnover of 2-bromotoluene and the dearomatisation product 6-ethyl-6-methylcyclohex-2,4-dienone was generated from the oxidation of 2-ethyltoluene. The RLYF/A330P variant altered the product distribution enabling the generation of certain metabolites in higher quantities. Using this variant produced 4-methyl-2-ethylphenol from 3-ethyltoluene with ≥90 % selectivity and with a biocatalytic activity suitable for scale-up of the reaction.
- Munday, Samuel D.,Dezvarei, Shaghayegh,Lau, Ian C.-K.,Bell, Stephen G.
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p. 2512 - 2522
(2017/07/12)
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- The discovery of a novel route to highly substituted -tropolones enables expedient entry to the core of the gukulenins
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A simple and general method for the synthesis of highly substituted α-tropolone ethers that allows rapid access to the bis(tropolone) core of the antiproliferative metabolites (-)-gukulenins A and F (3, 4) is described. The reaction proceeds by thermolyti
- Kats-Kagan, Roman,Herzon, Seth B.
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supporting information
p. 2030 - 2033
(2015/04/27)
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- One-Pot Defunctionalization of Lignin-Derived Compounds by Dual-Functional Pd50Ag50/Fe3O4/N-rGO Catalyst
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Generation of hydrogen from renewable sources and its safe utilization for efficient one-pot upgrading of renewable biofuels are a challenge. Bimetallic PdAg catalyst supported on Fe3O4/nitrogen-doped reduced graphene oxide (N-rGO) were synthesized for hydrogen generation from formic acid with high TOF (497 h-1 at 50 °C), and the hydrogen was subsequently utilized in situ for selective defunctionalization of lignin-derived chemicals with preserved aromatic nature at ambient pressure. Hydrodeoxygenation of aromatic aldehydes and ketones gave excellent yields (99% at 130 °C) with no use of additives. Furthermore, hydrogenolysis of β-O-4 and α-O-4 C-O model compounds produced only two products with high selectivity at 120 °C, which is an efficient and versatile one-pot platform for valorization of lignin biomass.
- Singh, Ajay K.,Jang, Seungwook,Kim, Jae Yul,Sharma, Siddharth,Basavaraju,Kim, Min-Gyu,Kim, Kyung-Rok,Lee, Jae Sung,Lee, Hong H.,Kim, Dong-Pyo
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p. 6964 - 6972
(2015/11/18)
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- Method for producing alkoxy-hydroxybenzaldehyde that is substantially free of alkyl-alkoxy-hydroxybenzaldehyde
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The invention relates to a method for producing at least one alkoxy-hydroxybenzaldehyde (AHBA) from at least one hydroxyphenol (HP), said method being characterised in that it comprises the formation of at least one alkoxyphenol (AP) and alkyl-alkoxyphenol (AAP) and the separation (S) of AP from AAP, said separation (S) being carried out prior to obtaining AHBA.
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Paragraph 0265-0313
(2015/07/27)
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- Access to 3-arylindoles through a tandem one-pot protocol involving dearomatization, a regioselective michael addition reaction, and rearomatization
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A facile, general and rapid protocol for the introduction of oxygenated aryls at the 3-position of indoles is described. This approach consists of a tandem dearomatization, a regioselective Michael addition reaction, and rearomatization in a one-pot three-step sequence to obtain 3-arylindoles in good yields. A non-metal mediated detour method for installing oxygenated aryls at the 3-position of indoles is described. Copyright
- Chittimalla, Santhosh Kumar,Bandi, Chennakesavulu,Putturu, Sireesha,Kuppusamy, Rajesh,Boellaard, Kevin Christopher,Tan, David Chu Aan,Lum, Demi Ming Jie
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p. 2565 - 2575
(2014/05/06)
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- Correlating lignin structural features to phase partitioning behavior in a novel aqueous fractionation of softwood Kraft black liquor
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In this work, a set of softwood lignins were recovered from a Kraft black liquor using a novel pH-based fractionation process involving sequential CO 2 acidification and separation of the solvated aqueous lignin fraction. These recovered lignin fractions were characterized with respect to properties that may be responsible for their phase partitioning behavior as well as properties that may render the lignins more suitable for materials applications. Lignin fractions were recovered between a pH range of 12.8 and 9.5 with the bulk of the lignin (90%) recovered between a pH of 11.1 and 10.0. While all the fractions were found to consist primarily of lignin as validated by sample methoxyl content, the first fractions to phase separated were found to be especially enriched in aliphatic extractives and polysaccharides. From the bulk of the lignin that was recovered between a pH of 11.1 and 10.0 a number of noteworthy trends were discernible from the data. Specifically, the phenolic hydroxyl content was found to exhibit a strong negative correlation to the fractionation pH and exhibited a nearly 50% increase with recovery at decreasing pH, while the GPC-estimated molecular weights and 13C NMR-estimated β-O-4 content showed strong positive correlations to the pH at recovery. The aliphatic hydroxyl content exhibited minimal differences between recovery conditions. Overall, these results suggest that this fractionation approach can generate lignin fractions enriched in select physical or structural properties that may be important for their application as feedstocks for renewable chemicals or materials.
- Stoklosa, Ryan J.,Velez, Julian,Kelkar, Shantanu,Saffron, Christopher M.,Thies, Mark C.,Hodge, David B.
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supporting information
p. 2904 - 2912
(2013/10/08)
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- Vanillin and o-vanillin oligomers as models for dendrimer disassembly
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Linear analogs have been synthesized to model disassembling dendrimers. These linear analogs provide a facile synthesis to molecules that can be used to test new trigger groups and cleavage vectors. Vanillin and o-vanillin were used as the monomer units of these analogs and two trigger groups, allyl and o-nitrobenzyl, were chosen to test the disassembly process. Allyl triggered analogs 1a-d and 3a-d and o-nitrobenzyl triggered analogs 2a-c and 4a-c showed good to excellent disassembly as followed by the evolution of p-nitrophenoxide reporter ion by UV-Visible spectroscopy. The rate and yield of disassembly was shown to depend on experimental conditions as well as length of the cleavage vector.
- Kevwitch, Robert M.,Shanahan, Charles S.,McGrath, Dominic V.
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experimental part
p. 492 - 505
(2012/03/22)
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- PRODUCTION OF SUBSTITUTED PHENYLENE AROMATIC DIESTERS
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Synthesis pathways for a precursor to 5 -tert-butyl-3-methyl-1, 2-phenylene dibenzoate are provided. The precursor is methylcatechol and/or 5-tert-butyl-3-methylcatechol.
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Page/Page column 16-17
(2012/10/18)
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- First total synthesis of antrocamphin A and its analogs as anti-inflammatory and anti-platelet aggregation agents
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Naturally occurring antrocamphin A (1) is a potent anti-inflammatory compound from the edible fungus Antrodia camphorata (Taiwanofungus camphoratus), whose wild fruiting body is used as a valuable folk medicine in Taiwan. This study is the first total syn
- Lee, Chia-Lin,Huang, Chi-Huan,Wang, Hui-Chun,Chuang, Da-Wei,Wu, Ming-Jung,Wang, Sheng-Yang,Hwang, Tsong-Long,Wu, Chin-Chung,Chen, Yeh-Long,Chang, Fang-Rong,Wu, Yang-Chang
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supporting information; experimental part
p. 70 - 73
(2011/02/23)
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- Synthesis of the carbocyclic core of zoanthenol: Implementation of an unusual acid-catalyzed cyclization
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(Chemical Equation Presented) A smokin' hot cyclization! When the racemic cyclization precursor is heated in neat trifluoroacetic acid, an unusual Friedel-Crafts-type cyclization forms the carbocyclic core of the marine alkaloid zoanthenol containing two
- Behenna, Douglas C.,Stockdill, Jennifer L.,Stoltz, Brian M.
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p. 4077 - 4080
(2008/03/12)
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- Facile and regioselective dealkylation of alkyl aryl ethers using niobium(V) pentachloride
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A simple and facile method for the cleavage of carbon-oxygen bonds promoted by niobium pentachloride(V) is described. Excellent yields and regioselectivities were observed with various alkyl aryl ethers to give the phenols. NMR studies revealed the formation of monoaryloxy niobium salt(V), and a neighboring-group effect may play a significant role in the regioselectivity. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Sudo, Yukinori,Arai, Shigeru,Nishida, Atsushi
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p. 752 - 758
(2007/10/03)
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- QSAR study for?a?novel series of?ortho disubstituted phenoxy analogues of?α1-adrenoceptor antagonist WB4101
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On the basis of the affinities at the α1a-, α1b- and α1d-adrenoceptors and the 5-HT1A receptor of a previous series of sixteen 2-[(2-phenoxyethyl)aminomethyl]-1,4-benzodioxanes ortho monosubstituted at the pheno
- Pallavicini,Fumagalli,Gobbi,Bolchi,Colleoni,Moroni,Pedretti,Rusconi,Vistoli,Valoti
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p. 1025 - 1040
(2007/10/03)
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- Iron in the service of chromium: The ortho-benzannulation of trans,trans-dienyl Fischer carbene complexes
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Chromium Fischer carbene complexes with trans,trans-dienyl substituents on the carbene carbon will react with diiron nonacarbonyl to give 2-alkoxycyclohexa-2,4-dienone iron tricarbonyl complexes and/or 2-alkoxyphenols in excellent yields. In the presence
- Lian, Yiqian,Wulff, William D.
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p. 17162 - 17163
(2007/10/03)
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- A simple and regioselective carbon-oxygen bond cleavage using Niobium(V)
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A simple and convenient method for the differentiation of alkoxy groups on aromatic rings is described. Niobium(V) is found to possess a strong Lewis acid property to transform alkyl arylethers smoothly to the corresponding phenols in high yields. The excellent regioselectivity was also observed in dialkoxy benzene derivatives under mild conditions.
- Arai, Shigeru,Sudo, Yukinori,Nishida, Atsushi
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p. 1104 - 1106
(2007/10/03)
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- BISPHOSPHINE, PROCESS FOR PRODUCING THE SAME, AND USE THEREOF
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Bisphosphines represented by the general formula (I) wherein Ar1 and Ar2 each represents an arylene group which may be substituted; R1 and R2 each represents an alkyl group which may be substituted, or an aryl group which may be substituted, or R1 and R2 may combinedly form a ring together with the phosphorus atom bonded thereto; R3 and R4 each represents hydrogen atom or an alkyl group; and the carbon atoms each having R3 and R4 are bonded in positions ortho to the oxygen atom bonded to Ar1 and Ar2: process for production thereof; Group VIII metal complexes comprising said bisphosphines; and process for producing aldehydes, which comprises, on hydroformylation of ethylenically unsaturated compounds with carbon monoxide and hydrogen, using said Group VIII metal complexes.The hydroformylation of ethylenically unsaturated compounds according to the present invention can produce n-aldehydes at higher reaction rate and industrially more advantageously than with catalysts comprising conventional phosphines, while suppressing side reactions such as hydrogenation and isomerization.
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- Intermolecular Diels-Alder reactions of brominated masked o-benzoquinones with electron-deficient dienophiles. A detour method to synthesize bicyclo[2.2.2]octenones from 2-methoxyphenols
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Intermolecular Diels-Alder reactions of masked o-benzoquinones, i.e., 6,6-dimethoxy-2,4-cyclohexadienones 5-7 and 21-24 generated from 2-methoxyphenols 1-3 and 17-20, respectively, with electron-deficient dienophiles leading to highly functionalized bicyclo[2.2.2]octenones are described. The masked o-benzoquinones (MOBs) 5-7 underwent Diels-Alder cycloadditions with methyl acrylate, methyl methacrylate, and methyl vinyl ketone to provide bicyclo[2.2.2]octenones 13a-c to 15a-c (direct method) in low to moderate yields with the concomitant formation of considerable amounts of dimers 9-11. To retard dimerization and to improve the yields of the requisite bicyclo[2.2.2]octenones, a detour method comprised of sequential bromination of 2-methoxyphenols 1-4, oxidation and Diels-Alder reaction, and debromination has been developed. The oxidation of bromophenols 17-20 produced MOBs 21-24 which are stable enough to be isolated. The MOBs 21-24 underwent cycloaddition with electron-deficient dienophiles in a very efficient manner to afford the corresponding cycloadducts 25a-c to 28a-c in good to high yields without self-dimerization. When the cycloadducts 25a-c to 28a-c were treated with either Bu3SnH/AIBN or tributylammonium formate-palladium reagent, the corresponding debrominated products 13a-c to 16a-c were obtained in high to excellent yields. In general, the cycloadducts 13a-c to 15a-c were obtained in 20-40% higher yields via the detour method than those via the direct method. In both routes, the Diels-Alder reactions proceeded in a highly regio- and stereoselective manner to furnish a single cycloadduct in each case.
- Lai, Chien-Hsun,Shen, Yi-Ling,Wang, Min-Nen,Rao, N. S. Kameswara,Liao, Chun-Chen
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p. 6493 - 6502
(2007/10/03)
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- Isolation, Synthesis, Structure-Activity Relationships of Bioactive Benzoquinones from Miconia lepidota from the Suriname Rainforest
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Bioactivity-directed fractionation of an EtOAc extract from the leaves of Miconia lepidota afforded the two benzoquinones 2-methoxy-6-heptyl-1,4-benzoquinone (1) and 2-methoxy-6-pentyl-1,4-benzoquinone (primin) (2). This is the first reported isolation of
- Gunatilaka, A. A. Leslie,Berger, John M.,Evans, Randy,Miller, James S.,Wisse, Jan H.,Neddermann, Kim M.,Bursuker, Isia,Kingston, David G. I.
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- Flash vacuum pyrolysis of methoxy-substituted lignin model compounds
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The flash vacuum pyrolysis (FVP) of methoxy-substituted fi-O-4 lignin model compounds has been studied at 500 °C to provide mechanistic insight into the primary reaction pathways that occur under conditions of fast pyrolysis. FVP of PhCH2CH2OPh (PPE), a model of the dominant β-O-4 linkage in lignin, proceeds by C-O and C-C cleavage, in a 37:1 ratio, to produce styrene plus phenol as the dominant products and minor amounts of toluene, bibenzyl, and benzaldehyde. From the deuterium isotope effect in the FVP of PhCD2CH2OPh, it was shown that C-O cleavage occurs by homolysis and by 1,2- elimination in a ratio of 1.4:1, respectively. Methoxy substituents enhance the homolysis of the β-O-4 linkage, relative to PPE, in o-CH3O- C6H4OCH2CH2Ph (o-CH3O-PPE) and (o-CH3O)2-C6H3OCH2CH2Ph ((o- CH3O)2-PPE) by a factor of 7.4 and 21, respectively. The methoxy- substituted phenoxy radicals undergo a complex series of reactions, which are dominated by 1,5-, 1,6-, and 1,4-intramolecular hydrogen abstraction, rearrangement, and α-scission reactions. In the FVP of o-CH3O-PPE, the dominant product, salicylaldehyde, forms from the methoxyphenoxy radical by a 1,5-hydrogen shift to form 2-hydroxyphenoxymethyl radical, 1,2-phenyl shift, and β-scission of a hydrogen atom. The 2-hydroxyphenoxymethyl radical can also cleave to form formaldehyde and phenol in which the ratio of 1,2-phenyl shift to β-scission is ca. 4:1. In the FVP of o-CH3O-PPE and (o-CH3O)2- PPE, products (ca. 20 mol %) are also formed by C-O homolysis of the methoxy group. The resulting phenoxy radicals undergo 1,5- and 1,6-hydrogen shifts in a ratio of ca. 2:1 to the aliphatic or benzylic carbon, respectively, of the phenethyl chain. In the FVP of (o-CH3O)2-PPE, o-cresol was the dominant product. It was formed by decomposition of 2-hydroxy-3- hydroxymethylbenzaldehyde and 2-hydroxybenzyl alcohol, which are formed from a complex series of reactions from the 2,6-dimethoxyphenoxy radical. The key step in this reaction sequence was the rapid 1,5-hydrogen shift from 2- hydroxy-3-methoxybenzyloxy radical to 2-hydroxymethyl-6-methoxyphenoxy radical before β-scission of a hydrogen atom to give the substituted benzaldehyde. The 2-hydroxybenzyl alcohols rapidly decompose under the reaction conditions to o-benzoquinone methide and pick up hydrogen from the reactor walls to form o-cresol.
- Britt, Phillip F.,Buchanan III,Cooney, Mark J.,Martineau, Dan R.
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p. 1376 - 1389
(2007/10/03)
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- Sodium Bis(trimethylsily)amide and Lithium Diisopropylamide in Deprotection of Alkyl Aryl Ethers: α-Effect of Silicon
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Removal of methyl, benzyl, and methylene groups from alkyl aryl ethers is among the most popular deprotecting methods in organic synthesis. Alkali organoamides NaN(SiMe3)2 and LiN(i-Pr)2, often used as organic bases, have been developed as efficient deprotecting agents. Treatment of aryl methyl ethers with 1.5 equiv of NaN(SiMe3)2 or LiN(i-Pr)2 in THF and 1,3-dimethyl-2-imidazolidinone in a sealed tube at 185 °C produced the corresponding phenol derivatives in good to excellent yields (80-97percent). Removal of the methylene unit from benzodioxole derivatives was also accomplished by use of 2.5 equiv of these alkali organoamides. The corresponding catechols were obtained in 93-99percent yields. The activity of NaN(SiMe3)2 was proven lower than that of LiN(i-Pr)2; it is due to the steric congestion and the α-stabilizing effect of the silyl groups. Thus selective mono-O-demethylation of o-dimethoxybenzenes can be achieved by the use of NaN(SiMe3)2 but not LiN(i-Pr)2. O-Debenzylation of aryl benzyl ethers, however, can be accomplished by the use of LiN(i-Pr)2.
- Hwu, Jih Ru,Wong, Fung Fuh,Huang, Jiann-Jyh,Tsay, Shwu-Chen
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p. 4097 - 4104
(2007/10/03)
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- Skin sensitization to eugenol and isoeugenol in mice: Possible metabolic pathways involving ortho-quinone and quinone methide intermediates
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With the aim of providing further mechanistic insights into the mode of action of eugenol (4-allyl-2-methoxyphenol) and isoeugenol (4-propenyl-2- methoxyphenol), we have synthesized two series of modified compounds which were tested in the mouse local lym
- Bertrand, Franck,Basketter, David A.,Roberts, David W.,Lepoittevin, Jean-Pierre
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p. 335 - 343
(2007/10/03)
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- Preparation of naturally occurring anthraquinones
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Several anthraquinones, which occur in plants used to treat cancer in traditional Chinese Medicine, have been synthesized and tested for cytotoxicity in two mammalian cell lines.
- Zhang, Xiuguo,Fox, Brian W.,Hadfield, John A.
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- DNA cleavage by Di- and trihydroxyalkylbenzenes. Characterization of products and the roles of O2, Cu(II), and alkali
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Several 5-alkyl-1,3-dihydroxybenzene (5-alkylresorcinol, 1) and 6-alkyl-1,2,4-trihydroxybenzene (2) derivatives were prepared and used to study the mechanism by which such compounds effect Cu(II)-dependent DNA strand scission. Comparison of the methyl, n-pentyl, n-undecyl, and n-hexadecyl derivatives in each structural series indicated that the efficiency of DNA cleavage increased with increasing length of the alkyl substituent. DNA cleavage by the 5-alkylresorcinols appears to involve initial oxygenation of the benzene nucleus, a process that occurs readily at alkaline pH in the presence of Cu2+ and O2. The resulting trihydroxylated benzenes mediate DNA cleavage in a reaction dependent on the presence of both Cu2+ and O2. The mechanism appears to involve reduction of Cu2+ by the trihydroxybenzene moiety in 2, with subsequent formation of reactive oxygen species. The ability of catalase and dimethyl sulfoxide to suppress DNA strand scission is consistent with the intermediacy of H2O2 and ?OH in the DNA strand scission process.
- Singh, Udai S.,Scannell, Ralph T.,An, Haoyun,Carter, Barbara J.,Hecht, Sidney M.
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p. 12691 - 12699
(2007/10/03)
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- Synthesis of Side-Chain-Modified Analogues of the Allergen Primin
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Benzoquinones such as primin (2-methoxy-6-pentyl-1,4-benzoquinone) from Primula obconica HANCE (Primulaceae) are known to be strong sensitizers and thus the source of severe allergic contact dermatitis (cell-mediated type of allergy).In order to determine
- Koenig, Wilfried A.,Faasch, Holger,Heitsch, Holger,Colberg, Cornelia,Hausen, Bjoern M.
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p. 387 - 393
(2007/10/02)
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- Tobacco smoke chemistry. 2. Alkyl and alkenyl substituted guaiacols found in cigarette smoke condensate.
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A series of alkyl and alkenyl substituted guaiacols, which comprise a group of biologically and organoleptically active compounds, have been synthesized. Mass spectra and GC retention times for these have been recorded and compared with those obtained for constituents of a weakly acidic fraction of smoke condensate derived from American blend type cigarettes. On the basis of these results, 25 guaiacols have been identified, 18 of which have not been detected in tobacco smoke condensate previously.
- Arnarp,Bielawski,Dahlin,Dahlman,Enzell,Pettersson
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- Quassinoids. 2. A New Approach to the BCD Ring System
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Diels-Alder reaction of 2,6-disubstituted quinones 4 and simple dienes 5 furnished cis adducts 3 in good yields.Basic isomerization provided the trans-decalins 11 which were converted into the lactones 2 which are models of the BCD ring systems of quassin
- Stevens, Robert V.,Angle, Steven R.,Kloc, Ken,Mak, Kok F.,Trueblood, Kenneth N.,Liu, You-Xi
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p. 4347 - 4353
(2007/10/02)
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- Boron Trichloride as a Selective Demethylating Agent for Hindered Ethers: a Synthesis of the Phytoalexins α- and β-Pyrufuran, a Synthesis of Tri-O-methylleprolomin and its Demethylation
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Boron trichloride has been found to be an efficient reagent for the selective cleavage of sterically hindered methoxy groups in methoxyarenes.The scope and utility of this reaction are explored with examples drawn from derivatives of benzene, naphtalene, 9,10-dihydrophenanthrene and dibenzofuran.The method is applied to the synthesis of the phytoalexins α- (56) and β-pyrofuran (58) (1,3,4-trimethoxydibenzofuran-2-ol and 1,2,4-trimethoxydibenzofuran-3-ol).A synthesis of tri-O-methylleprolomin (61), a derivative of the unusual lichen metabolite leprolomin (60), is described and its demethylation with boron trichloride is studied.
- Carvalho, Christopher F.,Russo, Albert V.,Sargent, Melvyn V.
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p. 777 - 792
(2007/10/02)
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- SYNTHESIS OF 3-METHYLPYROCATECHOL AND ITS DIACETATE - INTERMEDIATES FOR PRODUCTION OF 3-METHYL-4,6-DINITROPYROCATECHOL (ANTIOXIDANT FOR FATS).
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The authors have devised simple methods for synthesizing compounds (III) (3-Methylpyrocatechol) and (3-Methylpyrocatechol diacetate) (IV) in high yields (75% of theoretical) by using a scheme from o-vanillin (I), and which is a by-product of vanillin manufacture. o-Vanillin is reduced under the conditions of the Kishner reaction by the method described in the literature. It is found that increase of the time of boiling of the mixture of compound (I) with hydrazine hydrate from 1-2 to 4 h, and of the time of heating of the reaction mixture at 140-145 degree (after addition of potassium hydroxide) from 0. 5-1 to 4 h, raises the yield of (II) (2-Methyl-6-methoxyphenol) from 82 to 90%. If this reaction is conducted in diethylene glycol solution or if the reduction is effected by amalgamated zinc and hydrochloric acid, compound (II) is obtained in yields of 70 and 45% respectively.
- Daukshas,Martinkus,Shal'tite,Udrenaite
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p. 2520 - 2521
(2007/10/02)
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- Boron Trichloride as a Selective Demethylating Agent for Hindered Ethers
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Boron trichloride has been found to be an efficient reagent for the selective cleavage of sterically hindered methoxy groups in methoxyarenes; the scope and utility of this reaction are explored.
- Carvalho, Christopher F.,Sargent, Melvyn V.
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p. 227 - 229
(2007/10/02)
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- SYNTHESIS OF 5-HALOGEN-SUBSTITUTED 2,3-DIHYDROXYPHENYLACETIC ACIDS, THEIR ESTERS, AND 2,3-DIMETHOXYPHENYLACETOHYDROXAMIC ACIDS
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Many-stage general methods were developed for the synthesis of 5-bromo- or 5-chloro-substituted 2,3-dimethoxyphenylacetic acids from o-vanilin.Methods were also developed for their conversion into the corresponding hydroxamic acids, 2,3-dihydroxyphenylace
- Daukshas, V. K.,Martinkus, R. S.,Kuleshyus, V. A.,Shtel'bene, V. P.
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p. 458 - 463
(2007/10/02)
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- COMPETITION BETWEEN NUCLEAR AND SIDE-CHAIN SUBSTITUTION IN THE OXIDATION OF SOME ALKYLAROMATIC COMPOUNDS BY CERIUM(IV) AMMONIUM NITRATE AND COBALT(III) ACETATE
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The distribution between nuclear and side-chain substitution (N:S ratio) in the oxidations of m-methoxytoluene, 2-methylnaphtalene, mesitylene, and fluorene by cerium(IV) ammonium nitrate (CAN) and cobalt(III) acetate in acetic acid has been determined.The two oxidants exhibit remarkably different behaviours, the propensity for nuclear substitution being much stronger with CAN than with Co(OAc)3.For example, with m-methoxytoluene, CAN affords only products of nuclear acetoxylation, whereas Co(OAc)3 gives side-chain acetoxylation exclusively.The N:S ratio and the isomeric distribution for the CAN-induced reactions are consistent with a mechanism involving a common radical cation intermediate for the side-chain and nuclear substitution.The same mechanism might hold in the reactions with Co(OAc)3; however, in this case, the simultaneous operation of two different mechanisms is an additional possibility: a radical cation mechanism for the nuclear substitution and a hydrogen atom transfer mechanism for the side-chain reaction.
- Baciocchi, Enrico,Rol, Cesare,Sebastiani, Giovanni V.
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p. 513 - 518
(2007/10/02)
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