- Coumarin-related compounds as plant growth inhibitors from two rutaceous plants in Thailand
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Chemical investigation of naturally occurring plant growth inhibitors from Rutaceous plants in Thailand led us to identify five 7-methoxycoumarins and one 5,7-dimethoxycoumarin from Murraya paniculata, and six furanocoumarins from Citrus aurantifolia. Of these compounds, murranganon senecioate (1) is a new natural compound found in M. paniculata. Minumicrolin (6) was found to be highly active against the 2nd leaf sheath elongation of rice seedlings.
- Jiwajinda, Suratwadee,Santisopasri, Vilai,Ohigashi, Hajime
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Read Online
- Effect of Differential Geminal Substitution of γAmino Acid Residues at the (i + 2) Position of αγTurn Segments on the Conformation of Template β-Hairpin Peptides
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The effect of insertion of three geminally dimethyl substituted γamino acid residues [γ2,2 (4-amino-2,2-dimethylbutanoic acid), γ3,3 (4-amino-3,3-dimethylbutanoic acid), and γ4,4 (4-amino-4,4-dimethylbutanoic acid)] at the (i + 2) position of a two-residue αγC12 turn segment in a model octapeptide sequence Leu-Phe-Val-Aib-Xxx-Leu-Phe-Val (where Xxx = γamino acid residues) has been investigated in this study. Solution conformational studies (NMR, CD, and IR) and ab initio calculations indicated that γ3,3 and γ4,4 residues were well accommodated in the β-hairpin nucleating αγC12 turns, which gave rise to well-registered hairpins, in contrast to γ2,2, which was unable to form a tight C12 β-hairpin nucleating turn and promote a well-registered β-hairpin. Geminal disubstitution at the Cα carbon in γ2,2 led to unfavorable steric contacts, disabling its accommodation in the αγC12 hairpin nucleating turn unlike the γ3,3 and γ4,4 residues. Geminal substitutions at different carbons along the backbone constrained backbone torsion angles for the three γamino acid residues differently, generating diverse conformational preferences in them. Folded hairpins were energetically more stable (~8 to 9 kcal/mol) than the unfolded peptides. Conformational preference of the peptides was independent of the N-terminal protecting group. Such fundamental understanding will instrumentalize the future directed design of foldamers.
- Chatterjee, Sunanda,Debnath, Swapna,Ghosh, Suvankar,Pandit, Gopal,Satpati, Priyadarshi
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supporting information
p. 11310 - 11323
(2021/09/07)
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- N-Heterocyclic Carbene/Carboxylic Acid Co-Catalysis Enables Oxidative Esterification of Demanding Aldehydes/Enals, at Low Catalyst Loading
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We report the discovery that simple carboxylic acids, such as benzoic acid, boost the activity of N-heterocyclic carbene (NHC) catalysts in the oxidative esterification of aldehydes. A simple and efficient protocol for the transformation of a wide range of sterically hindered α- and β-substituted aliphatic aldehydes/enals, catalyzed by a novel and readily accessible N-Mes-/N-2,4,6-trichlorophenyl 1,2,4-triazolium salt, and benzoic acid as co-catalyst, was developed. A whole series of α/β-substituted aliphatic aldehydes/enals hitherto not amenable to NHC-catalyzed esterification could be reacted at typical catalyst loadings of 0.02–1.0 mol %. For benzaldehyde, even 0.005 mol % of NHC catalyst proved sufficient: the lowest value ever achieved in NHC catalysis. Preliminary studies point to carboxylic acid-induced acceleration of acyl transfer from azolium enolate intermediates as the mechanistic basis of the observed effect.
- Berkessel, Albrecht,Biswas, Animesh,Harnying, Wacharee,Sudkaow, Panyapon
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supporting information
p. 19631 - 19636
(2021/08/09)
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- Engineering Catalysts for Selective Ester Hydrogenation
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The development of efficient catalysts and processes for synthesizing functionalized (olefinic and/or chiral) primary alcohols and fluoral hemiacetals is currently needed. These are valuable building blocks for pharmaceuticals, agrochemicals, perfumes, and so forth. From an economic standpoint, bench-stable Takasago Int. Corp.'s Ru-PNP, more commonly known as Ru-MACHO, and Gusev's Ru-SNS complexes are arguably the most appealing molecular catalysts to access primary alcohols from esters and H2 (Waser, M. et al. Org. Proc. Res. Dev. 2018, 22, 862). This work introduces economically competitive Ru-SNP(O)z complexes (z = 0, 1), which combine key structural elements of both of these catalysts. In particular, the incorporation of SNP heteroatoms into the ligand skeleton was found to be crucial for the design of a more product-selective catalyst in the synthesis of fluoral hemiacetals under kinetically controlled conditions. Based on experimental observations and computational analysis, this paper further extends the current state-of-the-art understanding of the accelerative role of KO-t-C4H9 in ester hydrogenation. It attempts to explain why a maximum turnover is seen to occur starting at 25 mol % base, in contrast to only 10 mol % with ketones as substrates.
- Dub, Pavel A.,Batrice, Rami J.,Gordon, John C.,Scott, Brian L.,Minko, Yury,Schmidt, Jurgen G.,Williams, Robert F.
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p. 415 - 442
(2020/03/04)
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- Direct and Tandem Routes for the Copolymerization of Ethylene with Polar Functionalized Internal Olefins
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Transition metal catalyzed ethylene copolymerization with polar monomers is a highly challenging reaction. After decades of research, the scope of suitable comonomer substrates has expanded from special to fundamental polar monomers and, recently, to 1,1-disubstituted ethylenes. Described in this contribution is a direct and tandem strategy to realize ethylene copolymerization with various 1,2-disubstituted ethylenes. The direct route is sensitive to sterics of both the comonomers and the catalyst. In the tandem route, ruthenium-catalyzed ethenolysis can convert 1,2-disubstituted ethylenes into terminal olefins, which can be subsequently copolymerized with ethylene to afford polar functionalized polyolefins. The one-pot, two-step tandem route is highly versatile and efficient in dealing with challenging substrates. This work is a step forward in terms of expanding the substrate scope for transition metal catalyzed ethylene copolymerization with polar-functionalized comonomers.
- Chen, Min,Chen, Changle
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supporting information
p. 1206 - 1210
(2019/12/24)
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- Cyanide-Free One-Pot Synthesis of Methacrylic Esters from Acetone
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Methacrylic esters, represented by methyl methacrylate (MMA), are widely used as commodity chemicals. Here, the one-pot synthesis of methacrylic esters from acetone, a haloform and alcohols in the presence of an organic base is described. Using DBU as the organic base for the reaction of acetone, chloroform and methanol in acetonitrile afforded MMA in 66 % yield. When the solvent was replaced by benzonitrile, the product MMA was successfully purified by distillation. Applicability of this process to various alcohols was also investigated to show ethyl, phenyl, CF3CH2, and n-C6F13CH2CH2 esters were obtained in moderate yields. The use of bromoform instead of chloroform resulted in the improvement of the yield, for example, methyl and n-C6F13CH2CH2 esters up to 81 and 70 %, respectively. The reaction with deuterated starting materials acetone-d6 and MeOH-d4, with DBU in acetonitrile afforded deuterated MMA (MMA-d8) in 70 % yield.
- Koyama, Minoru,Kawakami, Takafumi,Okazoe, Takashi,Nozaki, Kyoko
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p. 10913 - 10917
(2019/08/02)
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- Synthesis method of methyl senecioate
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The invention discloses a synthesis method of methyl senecioate. The synthesis method takes 1,3-propane sultone, methylimidazole, senecioic acid, methanol, aluminum hydroxide powder, citric acid, nickel nitrate and ammonium metatungstate as main raw materials; a synthesis technology provided by the invention takes senecioic acid and methanol to be subjected to esterification reaction under the action of a catalyst NiW/Al-CA to obtain methyl senecioate; in a preparation process of the catalyst, citric acid is added and used as organic acid to weaken a mutual effect between a metal component anda carrier; when the quantity of carboxyl groups of an organic acid molecule is greater, the mutual effect between active metal and the carrier is more obvious; compared with a traditional synthesis method, the synthesis method has the advantages that the catalyst is easy to separate and recycle and the environment pollution is reduced; a target product is synthesized in one step, side reaction isreduced and post-treatment steps are simplified; the yield of products is greatly improved.
- -
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Paragraph 0007; 0009-0017; 0028
(2018/10/19)
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- Synthesis method of ciclopirox olamine
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The invention discloses a synthesis method of ciclopirox olamine. The synthesis method includes following steps: (1), preparing dimethyl methacrylate; (2), preparing cyclohexane formyl chloride; (3), preparing 5-oxo-3-methyl-5-cyclohexyl-3-methyl pentenoate; (4), preparing 1-hydroxy-4-methyl-6-cyclohexyl-2(1H)-pyridone; (5), preparing 1-hydroxy-4-methyl-6-cyclohexyl-2(1H)-pyridone-2-amino-ethylate ciclopirox olamine. The synthesis method has the advantages of high yield, high product quality, low running cost, automatic running of equipment, high stability and easiness in meeting industrial needs.
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Paragraph 0050; 0051
(2017/12/29)
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- DMAP-Catalyzed [4 + 2] Cycloaddition of α,β-Unsaturated Carboxylic Acids with Ketones for Synthesis of α,β-Unsaturated δ-Lactones
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The DMAP-catalyzed [4 + 2] cycloaddition of α,β-unsaturated carboxylic acids with ketones furnishing α,β-unsaturated δ-lactones in good yields (up to 80%) is described, which is the first example of remote γ-C(sp3)-H activation of α,β-unsaturated carboxylic acids facilitated by DMAP, a pyridine-based catalyst. Copyright
- Jin, Jinghai,Xu, Qinchang,Deng, Weiping
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supporting information
p. 397 - 400
(2017/04/27)
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- Mukaiyama aldol reactions catalyzed by a trimeric organo aluminum(III) alkoxide
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Mukaiyama aldol reactions of enol ethers with a variety of aldehydes and ketones are efficiently catalyzed at 0-25 °C by the sterically bulky trimeric organo aluminum(III) alkoxide 1 synthesized via the reaction of 3 equiv of AlMe3 with tripodal tris(2-hydroxy-3-tert-butyl-5-methylphenyl) methane and the elimination of 3 equiv of methane. Comparisons of its catalytic properties with the less sterically hindered analogue 2, the more sterically hindered analogue 3, a monomeric aluminum near-analogue 4, and a dimeric alumatrane 5 revealed that 1 possesses superior activity.
- Kim, So Han,Yoon, Sungwoo,Kim, Youngjo,Verkade, John G.
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p. 1193 - 1206
(2014/09/30)
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- Enantioselective Rh-catalyzed hydrogenation of 3-aryl-4-phosphonobutenoates with a P-stereogenic BoPhoz-type ligand
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A series of chiral 3-aryl-4-phosphonobutyric acid esters were synthesized in high enantioselectivities (93-98% ee) via the Rh-catalyzed asymmetric hydrogenation of the corresponding 3-aryl-4-phosphonobutenoates using a P-stereogenic BoPhoz-type phosphine-aminophosphine ligand. The methodology has been successfully applied to the asymmetric synthesis of a potential GABA B antagonist, (R)-phaclofen, in high enantioselectivity.
- Duan, Zheng-Chao,Hu, Xiang-Ping,Zhang, Cheng,Zheng, Zhuo
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supporting information; experimental part
p. 8319 - 8321
(2011/03/17)
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- Surprising secondary photochemical reactions observed on conventional photolysis of diazotetrahydrofuranones
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The formation of C-H insertion products of the terminal N-atom of a diazo group into the α-S{cyrillic}N{cyrillic}-bond of tetrahydrofuran during direct photolysis of regioisomeric 2,2-dimethyl-5,5-diphenyl and 5,5-dimethyl-2,2-diphenyl-substituted 3-diazotetrahydrofuran-4-ones in THF is dictated by photochemical cycloelimination of the originally formed (1,1-dimethyl-2-oxa-3,3-diphenyl-propano)ketene and oxetanecarboxylic acid derivatives to yield benzophenone. The latter, under subsequent UV irradiation of the reaction mixture, initiates sensitized photolysis of the starting diazoketones resulting in the appearance of the insertion products with the solvent.
- Nikolaev, Valerij A.,Galkina, Olesja S.,Sieler, Jochim,Rodina, Ludmila L.
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experimental part
p. 2713 - 2716
(2010/06/19)
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- Novel strategies for the synthesis of anthrapyran antibiotics: Discovery of a new antitumor agent and total synthesis of (S)-espicufolin
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Two high-yielding strategies for the synthesis of 4H-anthra[1,2-b]pyran antibiotics have been developed giving access to novel antitumor agent 24 (ED50 1.5 m) and to (S)-espicufolin (3). A key step for the assembly of the tetracyclic 4H-anthra[1,2-b]pyran-4,7,12-trione skeleton is the nucleophilic addition of an aryl lithium species onto an aldehyde which allows the introduction of either an ynone or 1,3-diketo side chain, serving as precursors for an acid-catalysed cyclisation. The Royal Society of Chemistry.
- Tietze, Lutz F.,Gericke, Kersten M.,Singidi, Ramakrishna Reddy,Schuberth, Ingrid
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p. 1191 - 1200
(2008/02/04)
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- Antifungal activity of 4-methyl-6-alkyl-2H-pyran-2-ones
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A number of 4-methyl-6-alkyl-α-pyrones were synthesized and characterized on the basis of 1H NMR and mass spectroscopy. These compounds were tested in vitro against pathogenic fungi, namely, Sclerotium rolfsii Saccardo, Rhizoctonia bataticola (Taub.) Butler, Pythium aphanidermatum (Edson) Fitz., Macrophomina phaseolina (Tassi), Pythium debaryanum (Hesse), and Rhizoctonia solani Nees. Lower homologues were less effective, whereas compounds such as 4-methyl-6-butyl-α-pyrone, 4-methyl-6-pentyl-α-pyrone, 4-methyl-6-hexyl-α-pyrone, and 4-methyl-6-heptyl-α-pyrone were found effective against all of the test fungi. They inhibited mycelial growth by approximately 50% (ED50) at 15-50 μg/mL. 4-Methyl-6-hexyl-α- pyrone, which was found most effective, was tested against S. rolfsii in a greenhouse at 1, 5, and 10% concentrations. The 10% aqueous emulsion of 4-methyl-6-hexyl-α-pyrone suppressed disease development in tomato by 90-93% as compared with the untreated infested soil in the greenhouse after 35 days of treatment.
- Chattapadhyay, Tarun Kumar,Dureja, Prem
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p. 2129 - 2133
(2007/10/03)
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- Analysis of the volatile aroma constituents of parental and hybrid clones of pepino (Solanum muricatum)
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The volatile constituents of 10 clones (4 parents with different flavors and 6 hybrids from selected crossings among these parents) of pepino fruit (Solanum muricatum) were isolated by simultaneous distillation-extraction and analyzed by gas chromatography-mass spectrometry (GC-MS). Odor-contributing volatiles (OCVs) were detected by GC-olfactometry-MS analyses and included 24 esters (acetates, 3-methylbutanoates, and 3-methylbut-2-enoates), 7 aldehydes (especially hexenals and nonenals), 6 ketones, 9 alcohols, 3 lactones, 2 terpenes, β-damascenone, and mesifurane. Among these compounds, 17, of which 5 had not been reported previously in pepino, were found to contribute significantly to pepino aroma. OCVs can be assigned to three groups according to their odor quality: fruity fresh (acetates and prenol), green vegetable (C6 and C9 aidehydes), and exotic (lactones, mesifuran, and β-damascenone). Quantitative and qualitative differences between clones for these compounds are clearly related to differences in their overall flavor impression. The positive value found for the hybrid-midparent regression coefficient for volatile composition indicates that an important fraction of the variation observed is inheritable, which has important implications in breeding for improving aroma. Significant and positive correlations were found between OCVs having common precursors or related pathways.
- Rodriguez-Burruezo, Adrian,Kollmannsberger, Hubert,Prohens, Jaime,Nitz, Siegfried,Nuez, Fernando
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p. 5663 - 5669
(2007/10/03)
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- Quantum chemical calculations on the Peterson olefination with α-silyl ester enolates
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The reaction of stabilized Peterson reagents (α-silyl ester enolates) with ketones has been studied theoretically and experimentally. Enolate geometry was studied by trapping experiments and NMR spectroscopy and was found to differ markedly with the nature of the base (LiHMDS vs LDA vs KHMDS). The chelating effect of the lithium counterion was found to be critical for the reaction. For the two ketones studied, the combined weight of experimental and computational data assigns geometrical selectivity to the initial addition transition state, though in general there appears to be a fine balance between three possible choices for the rate-determining step.
- Gillies, Malcolm B.,Tonder, Janne E.,Tanner, David,Norrby, Per-Ola
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p. 7378 - 7388
(2007/10/03)
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- Solvent effect on alcoholysis rate of β,β-dimethylacryloyl chloride
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Data on methanolysis rate of β,β-dimethylacryloyl chloride in 22 solvents may be quantitatively correlated to the physico-chemical properties of solvents by five-parametric free energy equation. The rate is mainly affected by the basicity of the medium, since at increase thereof the reaction is retarded by competition for the acyl chloride molecule between the alcohol and the basic solvent.
- Marshalok,Oglashennyi,Makitra,Yatchishin,Pirig
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p. 1574 - 1580
(2007/10/03)
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- Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 15. Generation of alkoxycarbonyl(sulfenyl)carbenes and their intramolecular insertion to give alkenyl sulfides
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A range of 18 alkoxycarbonyl sulfinyl phosphorus ylides 9 have been prepared and their behaviour upon flash vacuum pyrolysis (FVP) at 600 deg C examined. For R1 = H, Me and Et they lose Ph3PO and in some cases Ph3P to give mixtures of products including the alkenyl sulfides 10, the sulfides 11, the disulfides 12 and the thioesters 14. The alkenyl sulfides 10 most likely arise from intramolecular insertion of the alkoxycarbonyl sulfenyl carbenes resulting from loss off Ph3PO to produce β-lactones which then lose CO2 and this is supported by the results from 13C labelled ylides. Possible mechanisms for the formation of 11 and 14 are also presented and the feasibility of various steps has been examined by preparation and pyrolysis of the proposed intermediates. In contrast, pyrolysis of the ylides 9 where R1 = Ph and the tert-butoxycarbonyl ylides 30 leads mainly to complete fragmentation with loss of Ph3PO and benzyl alcohol or 2-methylpropan-2-ol and does not give any useful sulfur-containing products. Four alkoxy-carbonyl sulfonyl diazo compounds 33 have been prepared and in three cases they give the alkenyl sulfones 34 upon FVP at 400 deg C, probably by an intramolecular insertion and decarboxylation process analogous to the formation of 10 from 9. On the other hand the alkoxycarbonyl carbenes produced by FVP of the amino acid-derived diazo compounds 35 undergo alternative proocesses with no sign of β-lactone formation. Fully assigned 13C NMR data are presented for 13 of the ylides.
- Aitken, R. Alan,Armstrong, Jill M.,Drysdale, Martin J.,Ross, Fiona C.,Ryan, Bruce M.
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p. 593 - 604
(2007/10/03)
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- Kinetics of alcoholysis of β,β-dimethylacryloyl chloride
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Rate constants and activation parameters have been determined for alcoholysis of β,β-dimethylacryloyl chloride with 14 alcohols in benzene at a reactant ratio of 1:1. The reaction proceeds via formation of H-complex or charge-transfer complex. Appropriate description of the effect of alcohol on the reaction rate requires simultaneous application of the Hammett-Taft and Koppel'-Pal'm equations.
- Marshalok,Oglashennyi,Makitra,Pirig,Yatchishin
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p. 1410 - 1418
(2007/10/03)
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- Thermodynamic properties of the esters of 3-methyl-2-butenoic acid
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The enthalpies of combustion of four esters of 3-methyl-2-butenoic acid were determined by bomb calorimetry. The temperature dependence of the saturated vapor pressure for the esters was studied with the tensimetry technique. The standard enthalpies of formation and vaporization for the esters were calculated.
- Van-Chin-Syan,Raevskii,Galatyn,Gerasimchuk,Kotovich
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p. 665 - 667
(2007/10/03)
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- Structure-cytoprotective activity relationship of simple molecules containing an α,β-unsaturated carbonyl system
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In previous reports we attributed the cytoprotective activity of several sesquiterpene lactones to the presence of a nonhindered electrophilic acceptor in their structure. We suggested that the mechanism of protection would be, at least in part, mediated through a reaction between the electrophilic acceptor and the sulfhydryl-containing groups of the mucosa. We report here the gastric cytoprotective effect of simple molecules containing an α,β-unsaturated carbonyl group. In the present paper, we undertake the study of molecular accessibility and molecular shape, in addition to conformational, electronic, and steric factors. Our results helped to establish two important facts connecting chemical structure with cytoprotective effect. Firstly, an adequate molecular accessibility appears to be necessary to produce the biological response, and secondly, the α,β- unsaturated carbonyl system has to be included in a cyclic structure or, at least, in the proximity of a cyclic system.
- Rodríguez, Ana M.,Enriz, Ricardo D.,Santagata, Luis N.,Jáuregui, Esteban A.,Pestchanker, Mauricio J.,Giordano, Oscar S.
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p. 1827 - 1834
(2007/10/03)
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- Gastric cytoprotective activity of 2-cyclopenten-1-one and related compounds
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The cytoprotective activity of the isolated functional groups of several sesquiterpene lactones is reported. Among them the highest activity is shown by α-methylen-γ-butyrolactone and 2-cyclopenten-1-one. The activity shown by those Michael acceptors with a β carbon hindered by an alkyl substituent was always lower or almost null. A three-way mechanism of action is proposed: a) reduced glutathione synthesis, b) prostaglandin synthesis and c) mucosal glycoprotein synthesis.
- Maria,Wendel,Guardia,Guzman,Pestchanker,Guerreiro,Giordano
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p. 1784 - 1786
(2007/10/03)
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- Flash vacuum pyrolysis of tert-butyl β-ketoesters: Sterically protected α-oxoketenes
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Infrared spectroscopic analysis of the products showed that flash vacuum pyrolyses (FVP) of dimethyl tert-butylmalonate (1b) and methyl tert-butyl(pivaloyl)acetate (1d) at ca. 550°C afforded the corresponding tert-butyl(carbomethoxy)ketene (4b) and tert-butyl(pivaloyl)ketene (4d), respectively, with loss of methanol, together with unreacted 1b and 1d (Ar matrix, 12 K or neat at 77 K; 10-5 mbar). Monitoring by IR spectroscopy showed that 4b reacted with methanol at ca. -50°C to give 1b. Ketene 4d does not react with methanol at room temperature, but afforded ester 1d on refluxing for 8 h. FVP of 1b and 1d at temperatures above 650°C gave the α-oxoketenes 4b and 4d, respectively, unsubstituted dimethyl malonate (1a) and methyl 4,4-dimethyl-3-oxo-pentanoate (1c), respectively, due to retro-ene reactions with elimination of isobutene, as well as pyrolysis products derived from 1a and 1c, respectively. FVP of α-unsubstituted β-ketoesters 1a and 1c at ca. 500°C (10-5 mbar) with argon matrix isolation of the products at 12 K afforded the ketenes 4a and 4c as mixtures of s-Z and s-E conformers together with mixtures of unreacted keto (1a, c) and enol forms (2a, c). On warming to temperatures between -90 and -50°C, back-reaction of ketenes 4a, c with methanol resulted in the re-generation of enols 2a, c without increasing the amounts of the keto forms 1a, c.
- Leung-Toung,Wentrup
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p. 7641 - 7654
(2007/10/02)
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- REACTIONS OF N-SILYLATED LACTAMS WITH α-BROMO CARBOXYLATES
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The reactions of N-trimethylsilyl lactams with α-bromo carboxylates proceeds in two directions: the N-alkylation of the lactams, and elimination with the formation of α,β-unsaturated carboxylic esters.The proportion between the two processes depends on the structure of the initial compounds.
- Orlova, N. A.,Shipov, A. G.,Baukov, Yu. I.
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p. 1877 - 1880
(2007/10/02)
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- REACTIONS OF N-CHLORO-N-ALKOXY-TERT-ALKYLAMINES WITH ISOBUTYLENE AND METHANOL
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The addition of N-chloro-N-methoxy-tert-alkylamines to an olefin, which is assumed to proceed with the participation of alkoxynitrenium ions, was carried out for the first time.The methanolysis of N-chloro-N-alkoxy-tert-alkylamines in the presence of Et3N gives dialkoxyamines, and depending on the type of the N-alkyl substituent is accompanied by side reactions.
- Shtamburg, V. G.,Rudchenko, V. F.,Grinev, V. M.,Dmitrenko, A. A.,Pleshkova, A. P.,Kostyanovskii, R. G.
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p. 951 - 954
(2007/10/02)
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- The Lactonization of 2'-Hydroxyhydrocinnamic Acid Amides: A Potential Prodrug for Amines
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The lactoniaztion of two hydroxy amides - 4-methoxyaniline 3-(2'-hydroxyphenyl)-3,3-dimethylpropionic acid amide (2b) and 4-methoxyaniline 3-(2'-hydroxy-4',6'-dimethylphenyl)-3,3-dimethylpropionic acid amide (3b) - was studied over a pH range of 1-8.Due to the slowness of its reaction, a third hydroxy amide - 4-methoxyaniline 3-(2'-hydroxyphenyl)propionic acid amide (1b) - was investigated only at pH values of 7.5 and 10.The lactonization of 2b and 3b, which was found to be subject to general catalysis by buffer components, was observed to be catalyzed concurrently but not concertedly by both the acidic and basic forms of the buffer.The buffer-independent pH rate profiles for the lactonization of 2b and 3b were found to obey the equation k0 = kH++> + kH2O + kOH-->, indicating that the reaction is also subject to specific catalysis by hydronium and hydroxide ions.A Broenstedt analysis of the rate constants for buffer catalysis gave α and β values of 0.30 +/- 0.02 and 0.54 +/- 0.04, respectively, for 3b.The rate constants for the accelerated lactonization of 1b at 50, 70, and 90 deg C and pH 10 were used to calculate values of 14.7 +/- 0.8 kcal/mol and -9.5 +/- 2.3 eu for the activation parameters, ΔH(excit.) and ΔS(excit.), respectively.Comparison of the observed rates of lactonization at pH 7.5 and 30 deg C for the three hydroxy amides allowed an estimate of the extent of rate enhancement provided by addition of a partial or total "trimethyl lock" for the hydroxy amide lactonization reaction under near physiological conditions.The order of reactivity of the three hydroxy amides was found to be 3b >> 2b > 1b with rate enhancement factors of 2.5E4, 44, and 1, respectively.This study was begun with the objective of generating a hydroxy amide of very high reactivity at physiological pH for development into amine prodrug forms. 3b, which exhibited a half-life of 65 s at pH 7.5, has been chosen for further development as an amine prodrug.
- Amsberry, Kent L.,Borchardt, Ronald T.
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p. 5867 - 5877
(2007/10/02)
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- Mechanism and Synthetic Applications of the Photochemical Generation and X-H Insertion Reactions of Oxacarbenes
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A kinetic study of the photochemical ring expansion of cyclobutanones to oxacarbenes has shown that, in the presence of alcohol, the oxacarbene is generated irreversibly.Substrates for the intramolecular versions of the oxacarbene generation-insertion sequence (heteroalkylcyclobutanones) were prepared by an intramolecular -Baeyer-Villiger sequence.These have been used to form 5-, 6-, 7-, and 8-membered nitrogen, oxygen, and sulfur bicyclic ring systems.
- Pirrung, Michael C.,Chang, Virginia K.,DeAmicis, Carl V.
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p. 5824 - 5831
(2007/10/02)
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- COPPER ION-PROMOTED ESTERIFICATIONS
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Esters are made from carboxylic acids on heating with an alkohol in the presence of a copper salt at 130 deg.
- Ho, Tse-lok
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p. 2897 - 2898
(2007/10/02)
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- Wittig Reactions of Ylide Anions derived from Stabilised Ylides
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Ester- and nitrile-stabilised ylide anions are more reactive than the corresponding ylides and react with aldehydes and ketones to give alkenes in good yields; the reactivity of stabilised triphenylphosphonium ylides is greatly increased by the replacement of one phenyl substituent.
- McKenna, Eugene G.,Walker, Brian J.
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p. 568 - 569
(2007/10/02)
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- SILVER-INDUCED RING-OPENING OF SOME TRI- AND TETRAHALOGENOCYCLOPROPANES
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Tri- and tetrahalogenated cyclopropanes (halogen = Br or Cl) undergo ring opening on reaction with silver perchlorate in methanol to produce methyl polyhalogenoallyl ethers or polyhalogenated dienes.
- Baird, Mark S.,Hussain, Heimi H.
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p. 2301 - 2312
(2007/10/02)
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- 172. β-Cleavage of Bis(homoallylic) Potassium Alkoxides. Two-Step Preparation of Propenyl Ketones from Carboxylic Esters. Synthesis of ar-Turmerone, α-Damascone, β-Damascone, and β-Damascenone
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The transformation of 36 bis(homoallylic) alcohols VII to alkenones IX and X via β-cleavage of their potassium alkoxides VIIa in HMPA has been investigated (cf.Scheme 2).These studies have established an order of β-cleavage for 2-propenyl, 1-methyl-2-propenyl, 2-methyl-2-propenyl, 1,1-dimethyl-2-propenyl, and benzyl groups in alkoxides 49a-56a and have allowed a comparison between the β-cleavage reaction and the oxy-Cope rearrangement in alkoxides 74a-83a.As illustrative synthetic applications, a two-step preparation of propenyl ketones 15-42 from carboxylic esters is described, together with syntheses of ar-turmerone (48), α-damascone ((E)-71), β-damascone ((E)-109), and β-damascenone ((E)-111).
- Snowden, Roger L.,Linder, Simon M.,Muller, Bernard L.,Schulte, Karl H.
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p. 1858 - 1878
(2007/10/02)
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- Nuclear Synthons: Mesyltriflone as an Olefin Polyanion Equivalent
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Mesyltriflone (CF3SO2CH2SO2CH3) is developed as a nuclear synthon reagent capable first of multiple constructions such as alkylations then of Ramberg-Baecklund elimination to a substituted olefin.The alkylations are clean and regiospecific, often amenable to one-pot operation, and in most cases the elimination is smooth.A variety of examples is presented to establish the scope of the method, and the mechanism and stereochemistry are discussed.
- Hendrickson, James B.,Boudreaux, Gerald J.,Palumbo, Paul S.
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p. 2358 - 2366
(2007/10/02)
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- ZINC (0) MEDIATED REGIO AND STEREOSELECTIVE COUPLING OF SUBSTITUTED BROMOCROTONATES
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A useful synthetic approach to 5-carbomethoxy-hepta-2,6-dienoates is reported, formally via Michael reaction with inverse electron demand.
- Orsini, F.,Pelizzoni, F.
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p. 169 - 178
(2007/10/02)
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- ALKALINE FLUORIDE-m-CHLOROPEROXYBENZOIC ACID SYSTEMS AS MODULATED OXIDATION REAGENTS: EPOXIDATION OF α,β-UNSATURATED ACETALS
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High yields (80-96percent) of epoxides of α,β-unsaturated acetals can be obtained by the use of suitable KF:NaF:m-CPBA mixtures as modulated oxidation reagents.
- Camps, Francisco,Coll, Jose,Messeguer, Angel,Pujol, Ferran
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p. 971 - 974
(2007/10/02)
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- Synthesis and Chemistry of 2,2,5,5-Tetramethylthiolane-3,4-dione. A Route to Bicyclopentyl-1-sulfonium Intermediates
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The reaction of sodium sulfide with 2,5-dibromo-2,5-dimethylhexane-3,4-dione affords in good yield 2,2,5,5-tetramethylthiolane-3,4-dione (3a).This material has been converted to a variety of derivatives, including 2,2,5,5-tetramethyl-3-diazothiolane-4-one (3b) and the corresponding sulfone derivative.Compound 3b on treatment with electrophiles undergoes rapid substitution by the electrophile at the diazo carbon.The reaction of 3b with bromine was shown, however, to follow an indirect course involving the formation of a bicyclopentyl-1-sulfonium ion as probable intermediate; this is opened reversibly by attack of bromide at sulfur at lower temperature, whereas irreversible attack at carbon adjacent to carbonyl occurs at higher temperatures.Evidence for an ylidic variant of the 1-thiabicyclopentyl structure was obtained from the thermal decomposition of 3b.No trace of a Wolff rearrangement product was obtained.In contrast, the sulfone 18, derived from 3b by oxidation, on thermolysis afforded 3,3-dimethyl-4-(2-propenyl)oxathiolan-5-one 2-oxide (47).This product was shown, by means of trapping experiments, to arise from the ketene derived by normal Wolff rearrangement of 18 without participation of sulfur.Various other transformations, including 1,3-dipolar cycloadditions, of 3b and other derivatives, were investigated.
- Bolster, John M.,Kellogg, Richard M.
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p. 4429 - 4439
(2007/10/02)
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- ADDITION OF CHLORINE, BROMINE AND BROMINE CHLORIDE TO SOME α,β-UNSATURATED METHYL ESTERS
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The additions of chlorine, bromine and bromine chloride to trans methyl 2-butenoate 1, trans methyl 2-methyl-2-butenoate 2 and methyl 3-methyl-2-butenoate 3 under ionic conditions were studied.Bromine chloride addition always gave as a major regioisomer the 2-bromo-3-chloro compound, almost quantitatively in the case of 3.The mechanism of bromonium ion ring-opening (SN1 or SN2) is discussed with respect to the double bond substitution and regioisomer proportions.The dihalo products were identified by MS, 1H and 13C NMR.
- Korhonen, Ilpo O. O.,Pitkaenen, Maija,Korvola, Jorma N. J.
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p. 2837 - 2841
(2007/10/02)
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- Cycloaddition of cyclopropanone acetals to tetracyanoethylene
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The cyclopropanone acetals 1a-e and tetracyanoethylene give in a thermal [σ2 + π2] cycloaddition 2,2,3,3-tetracyanocyclopentanone acetals 2a-e. In the case of 2-methylcyclopropanone acetal 1c the corresponding 5-methylcyclopentanone acetal 3c is also formed in minor amounts. With respect to the parent compound methyl substituents in the cyclopropane ring (1b-c,e) retard the cycloaddition reaction, whereas a phenyl group (1d) accelerates the reaction. The cycloadducts 2 are converted by water mainly into the ring-opened esters 4. The structures of compound 2 have been determined by 1H and 13C NMR.
- Wiering,Steinberg
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p. 1663 - 1666
(2007/10/02)
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- Rearrangement Chemistry of the α-Diazo Ketone Derived from 2,2,5,5-Tetramethylthiolane-3,4-dione
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The α-diazo ketone of 2,2,5,5-tetramethylthiolane-3,4-dione undergoes both thermally and photochemically induced rearrangement; the chief product, a thietanone derivative, undergoes smooth and rapid photochemically induced fragmentation.
- Bolster, J.,Kellogg, Richard M.
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p. 4804 - 4805
(2007/10/02)
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- Photochemical Cycloaddition of Singlet trans-Stilbene with α,β-Unsaturated Esters
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The photochemical cycloaddition reactions of singlet trans-stilbene with five α,β-unsaturated esters and diesters are described.Adduct stereochemistry is influenced more by secondary ?-orbital overlap than by steric effects.The reactivity of the unsaturated esters with singlet stilbene increases with their electron affinity.This trend is consistent with the formation of a charge-transfer-stabilized exciplex intermediate in which singlet stilbene is the electron donor.Cycloaddition quantum yields, however, decrease with increasing electron affinity.This trend isreadily explained by using simple frontier molecular orbital theory.
- Lewis, Frederick D.,DeVoe, Robert J.
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p. 948 - 951
(2007/10/02)
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