- Configurations of polyunsaturated sesterterpenoids from the diatom, Haslea ostrearia
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The partial configurations of C25 isoprenoid alkenes isolated from the diatom Haslea ostrearia Gaillon (Simonsen) have been established. A combination of NMR spectroscopy studies of the alkenes with chiral shift reagents in conjunction with soluble silver β-diketonate complexes and enantioselective gas chromatography of oxidation products of the alkenes was used. Unexpected differences in highly branched isoprenoid isomer configurations were observed between different laboratory cultures of the alga. (C) 2000 Elsevier Science Ltd.
- Johns, Lesley,Belt, Simon,Lewis, C. Anthony,Rowland, Steven,Masse, Guillaume,Robert, Jean-Michel,Koenig, Wilfried A.
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- Structure and reactivity in the hydrolyses of aliphatic carboxylic acid esters and chlorides
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For hexanoic acid and its seven isomers, relative rates have been determined for acid catalysed esterification with methanol, and compared with those for saponification of the methyl esters. A good correlation between logarithms of relative rates for the two reactions is obtained, and it is suggested that the eight isomers provide a test set of compounds in which steric effects alone act on reactivity at the acyl carbon. A full set of steric parameters (Es′ values) are presented. Rates of solvolyses of the acid chlorides- of the isomers have been determined conductometrically in 3:1 wt:wt acetonitrile water. Logarithms of relative rates show a poor correlation with Es′, and, taking into account the solvent dependence of the rates, the pattern excludes both rate-limiting formation of a tetrahedral intermediate and rate-limiting dissociation of chloride to form acylium ions. The remaining possibilities, a concerted process (ANDN?) and rapid reversible formation of a hydrate followed by rate-limiting dissociation of chloride (AN + DN?,) are considered. Copyright
- Regan, Andrew C.,Watt, C. Ian F.
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- Dehydrogenative Synthesis of Carboxylic Acids from Primary Alcohols and Hydroxide Catalyzed by a Ruthenium N-Heterocyclic Carbene Complex
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Primary alcohols have been reacted with hydroxide and the ruthenium complex [RuCl2(IiPr)(p-cymene)] to afford carboxylic acids and dihydrogen. The dehydrogenative reaction is performed in toluene, which allows for a simple isolation of the products by precipitation and extraction. The transformation can be applied to a range of benzylic and saturated aliphatic alcohols containing halide and (thio)ether substituents, while olefins and ester groups are not compatible with the reaction conditions. Benzylic alcohols undergo faster conversion than other substrates, and a competing Cannizzaro reaction is most likely involved in this case. The kinetic isotope effect was determined to be 0.67 using 1-butanol as the substrate. A plausible catalytic cycle was characterized by DFT/B3LYP-D3 and involved coordination of the alcohol to the metal, β-hydride elimination, hydroxide attack on the coordinated aldehyde, and a second β-hydride elimination to furnish the carboxylate.
- Santilli, Carola,Makarov, Ilya S.,Fristrup, Peter,Madsen, Robert
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p. 9931 - 9938
(2016/11/02)
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- Preparative isolation and structural characterization of sucrose ester isomers from oriental tobacco
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To date, the structures of the sucrose tetraester (STE) isomers, a main kind of sucrose esters (SEs) in Solanum, have not been conclusively assigned. In this study, three groups of STE isomers with the molecular weight 650, 664 and 678 (designated as STE I, STE II and STE III, respectively) have been isolated and purified from the oriental tobacco-Komotini Basma using a semi-preparative RP-HPLC method. The full characterization of the isomers in the three groups of STE were investigated for the first time by MS (HRMS, MS2) and NMR (1H, 13C, HSQC) spectroscopy combined with alkaline hydrolysis and STE derivation experiments. The STE III (a single compound) was confirmed as a known sucrose tetraester. Furthermore, the STE II was found to contain three isomers and the structures were first unambiguously established as 6-O-acetyl (2,3 or 2,4 or 3,4)-di-O-3-methylvaleryl-(4 or 3 or 2)-O-2-methylbutyryl-α-d-glucopyranosyl-β-d-fructofuranoside. Finally, the STE I was discovered to contain seven isomers and the structures were elucidated as 6-O-acetyl (2 or 3 or 4)-O-3-methylvaleryl-(3,4 or 2,4 or 2,3)-di-O-2-methylbutyryl-α-d-glucopyranosyl-β-d-fructofuranoside, 6-O-acetyl (2 or 3 or 4)-O-3-methylvaleryl-(3,4 or 2,4 or 2,3)-di-O-isovaleryl- α-d-glucopyranosyl-β-d-fructofuranoside and 6-O-acetyl (2,3 or 2,4 or 3,4)-di-O-3-methylvaleryl-(4 or 3 or 2)-O-isobutyryl-α-d-glucopyranosyl- β-d-fructofuranoside (one of the 3 isomers).
- Jia, Chunxiao,Wang, Yingying,Zhu, Yonghua,Xu, Chunping,Mao, Duobin
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- Phenylglycine methyl ester, a useful tool for absolute configuration determination of various chiral carboxylic acids
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A new chiral anisotropic reagent, phenylglycine methyl ester (PGME), developed for the elucidation of the absolute configuration of chiral α,α- disubstituted acetic acids, has turned out to be applicable to other substituted carboxylic acids, such as chiral α-hydroxy-, α-alkoxy-, and α- acyloxy-α,α-disubstituted acetic acids, as well as to chiral β,β- disubstituted propionic acids. Because a carboxylic moiety is convertible from other functional groups, e.g., ozonolysis of an olefin and oxidative cleavage of a glycol, the present findings can expand the utility of the PGME method to the absolute configuration determination of various types of organic compounds, even those which initially lack oxygen functions. Several examples of the combination of chemical reactions and the PGME method are described.
- Yabuuchi, Tetsuya,Kusumi, Takenori
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p. 397 - 404
(2007/10/03)
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- Highly stereoselective Lewis acid mediated conjugate radical additions to methyl α-D-glucopyranoside derivatives tethering an unsaturated ester moiety at C-4
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The Lewis acid mediated conjugate additions of alkyl radicals to some 4- crotonyl derivatives of methyl α-D-glucopyranoside proceeded with a high level of diastereochemical induction to provide the adducts carrying a β- chiral butanoic ester.
- Munakata, Ryosuke,Totani, Kiichiro,Takao, Ken-Ichi,Tadano, Kin-Ichi
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p. 979 - 982
(2007/10/03)
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- Smoking compositions
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This invention provides tobacco and non-tobacco smoking compositions which contain a heterocyclic-hydroxy-substituted carboxylate compound as a flavorant additive. In one of its embodiments, this invention provides tobacco compositions which contain a heterocyclic-hydroxy-substituted carboxylic acid flavorant additive such as 2-(2-butyl)-3-hydroxy-3-methyl-3-(3-pyridyl)propionic acid: STR1 Under smoking conditions the above illustrated heterocyclic-hydroxy-substituted carboxylate additive and its pyrolysis products flavor the mainstream and sidestream smoke.
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- Selective Oxidation of Alcohols and Aldehydes with Hydrogen Peroxide Catalyzed by Methyltrioctylammonium Tetrakis(oxodiperoxotungsto)phosphate(3-) under Two-Phase Conditions
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The use of methyltrioctylammonium tetrakis(oxodiperoxotungsto)phosphate(3-) (1c) in combination with hydrogen peroxide as the primary oxidant in an aqueous/organic biphase system provides a cheap, efficient, and versatile catalytic method for alcohol and aldehyde oxidation.By this method, a variety of water-insoluble primary and secondary alcohols and aldehydes were oxidized to carboxylic acids and ketones in good yields under mild conditions and after relatively short reaction times.
- Venturello, Carlo,Gambaro, Mario
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p. 5924 - 5931
(2007/10/02)
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- Direct Synthesis of Carboxylic Acids from Organoboranes
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Direct Synthesis of carboxylic acids through a two carbon atom homologation from organoboranes has been achieved, by the reaction with the dianion of phenoxyacetic acid.It is now possible to synthesize alkanoic, alkenoic, or alkynoic acids, from the corresponding alkenes, dienes, or enynes, respectively, via hydroboration.The reaction is tolerant of various functional groups present in alkenes, thus giving the corresponding carboxylic acids with chloro, sulfide, ether, acetal, and thioacetal functionalities in good yields.
- Hara, Shoji,Kishimura, Kotaro,Suzuki, Akira,Dhillon, Ranjit S.
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p. 6356 - 6360
(2007/10/02)
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- The Conversion of Aliphatic Primary Alcohols to the Corresponding Carboxylic Acids Using Calcium Hypochlorite
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The reaction of aliphatic primary alcohols with calcium hypochlorite in the presence of hydrochloric acid and excess tert-butanol produces the corresponding carboxylic acids in good yields.
- Kabalka, George W.,Chatla, Narayana,Wadgaonkar, Prakash P.,Deshpande, Sunil M.
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p. 1617 - 1623
(2007/10/02)
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- Electrophilic Additions to Alkynyl Tosylates. Formation of Vinyl 1,1-(Bis esters) and Related Compounds. X-ray Structure Determination of (E)-1-Chloro-1-(tosyloxy)-3,3-dimethyl-1-butene
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The reaction of alkynyl tosylates, RCCOTs, R=t-Bu, sec-Bu, with a variety of electrophiles, HCl, CF3COOH, CF3SO3H, ArSO3H, and H3O+, in CH2Cl2 is reported.Only regio- and stereospecific syn-monoaddition products were observed, yielding vinyl 1,1-(bis esters) and related compounds in good yields.The single-crystal X-ray data of the HCl adduct to t-BuCCOTs is reported.These results and their mechanistic implications are discussed.
- Stang, Peter J.,Roberts, Kenneth A.
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p. 5213 - 5217
(2007/10/02)
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- Synthese von optisch aktiven Trogoderma-Pheromonen durch Kolbe-Elektrolyse
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The (R)-(-)-enantiomers of (Z)- (1) and (E)-14-methyl-8-hexadecen-1-ol (2) have been synthesized by coelectrolysis of (R)-(-)-4-methylhexanoic acid (7) with 12-(tetrahydro-2-pyranyloxy)-4-dodecynoic acid (8) and its subsequent hydrogenation.The acid 7 was prepared in high optical purity from (S)-(-)-citronellol (3) by conversion of the hydroxyl group to a methyl substituent and subsequent cleavage of (R)-(-)-2,6-dimethyl-2-octene (4) with ozone.By alkylation of 4-pentynoic acid (5) with 1-bromo-7-(tetrahydro-2-pyranyloxy)heptane (6) the alkynoic acid 8 was synthesized.
- Jensen, Uta,Schaefer, Hans-J.
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p. 292 - 297
(2007/10/02)
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- THE SYTHESIS OF γ-FLUOROISOLEUCINE
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Condensation of 3-fluoro-2-butanone (2) with alkyl diethylphosphonoacetates (4a-d) gave alkyl 4-fluoro-3-methyl-2-pentenoates (5a-d).Addition of bromine yielded alkyl-2,3-dibromo-4-fluoro-3-methylpentanoates (6a,b) which were dehydrobrominated to alkyl 2-bromo-4-fluoro-3-methyl-2-pentenoates (7a,b).Since these compounds could not be hydrogenated to the desired alkyl 2-bromo-4-fluoro-3-methylpentanoates (8a,b), another route was taken.The esters 5a-d were hydrogenated to alkyl 4-fluoro-3-methylpentanoates (11a-c) which were converted to their carbanions.Treatment with bromine gave esters 8a-c, and iodine gave alkyl 4-fluoro-2-iodo-3-methylpentanoates (12a,b).Esters 8a-c and 12a,b were converted to alkyl 2-azido-4-fluoro-3-methylpentanoates (13a-c) whose hydrogenation gave alkyl 2-amino-4-fluoro-3-methylpentanoates (14a-c).Hydrolysis afforded γ-fluoroisoleucine (1).
- Butina, D.,Hudlicky, M.
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p. 301 - 324
(2007/10/02)
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