- Structure-Elucidating Total Synthesis of the (Polyenoyl)tetramic Acid Militarinone C §
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The (polyenoyl)tetramic acid militarinone C (1) heads a family of seven members. Before our work, the configuration of C-5 was unknown whereas the configurations of C-8′ and C-10′ were either (R,R) or (S,S). We synthesized the four stereoisomers of constitution 1, which conform with these insights. This included cross-coupling both enantiomers of the western building block (8) with both enantiomers of the eastern building block (9). The specific rotations of the resulting 1 isomers suggested that natural 1 is configured like the coupling partners (S)-8 and (R,R)-9. This conclusion was corroborated by degrading natural 1 to alcohol 35 and by proving its configurational identity with synthetic (R,R)-35.
- Brückner, Reinhard,Drescher, Christian,Hamburger, Matthias,Keller, Morris,Potterat, Olivier
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- Total synthesis and configurational validation of (+)-violapyrone C
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Gold(I)-catalyzed intramolecular 6-endo-dig cyclization of tert-butyl ynoates afforded α-pyrone cores of violapyrones. Moreover, this reaction was successfully applied to the stereospecific syntheses of (+)- and (-)-violapyrone C, which allowed the absolute configuration of natural (+)-violapyrone C to be assigned by comparison of the optical rotations. This first total synthesis, which proceeded in 22% yield over 10 steps from (S)-(-)-2-methylbutanol, features silver(I) oxide promoted monobenzylation of 1,4-butanediol, Wittig olefination, Claisen condensation, Corey-Fuchs reaction, and gold(I)-catalyzed α-pyrone synthesis. Copyright
- Lee, Jong Seok,Shin, Junho,Shin, Hee Jae,Lee, Hwa-Sun,Lee, Yeon-Ju,Lee, Hyi-Seung,Won, Hoshik
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supporting information
p. 4472 - 4476
(2014/08/05)
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- Pheromone synthesis. Part 245: Synthesis and chromatographic analysis of the four stereoisomers of 4,8-dimethyldecanal, the male aggregation pheromone of the red flour beetle, Tribolium castaneum
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All four stereoisomers of 4,8-dimethyldecanal (1) were synthesized from the enantiomers of 2-methyl-1-butanol and citronellal. Enantioselective GC analysis enabled separation of (4R,8R)-1 and (4R,8S)-1 from a mixture of (4S,8R)-1 and (4S,8S)-1, when octakis-(2,3-di-O-methoxymethyl-6-O-tert-butyldimethylsilyl)- γ-cyclodextrin was employed as a chiral stationary phase. Complete separation of the four stereoisomers of 1 on reversed-phase HPLC at -54 °C was achieved after oxidation of 1 to the corresponding carboxylic acid 12 followed by its derivatization with (1R,2R)-2-(2,3-anthracenedicarboximido) cyclohexanol, and the natural 1 was found to be a mixture of all the four stereoisomers.
- Akasaka, Kazuaki,Tamogami, Shigeyuki,Beeman, Richard W.,Mori, Kenji
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experimental part
p. 201 - 209
(2011/02/27)
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- Salts of Mosher's thioacid: agents for determining the enantiomer excess of SN2 substrates
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The racemic and the (S)-enantiomer of Mosher's thioacid, 2-methoxy-2-trifluoromethylphenylacetic thioacid, form air-stable salts with Proton Sponge [1,8-bis(dimethylamino)naphthalene]. These salts are powerful nucleophiles that react cleanly (SN2 inversion) in CDCl3 with optically active alkyl halides ranging in reactivities from unactivated alkyl bromides and iodides to benzylic bromides. The diastereomeric excess (de) of the thioester products indicates the enantiomeric excess (ee) of the starting alkyl halides.
- Richman, Jack E.
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supporting information; experimental part
p. 2793 - 2796
(2010/07/06)
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- Stereoisomeric indole compounds, process for the preparation of the same, and use thereof
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Novel stereoisomeric indole compounds of the formula (1), a process for the preparation the same, and use thereof wherein, Y represents the group wherein, X represents alkyl group having 1-5 carbon atom(s) (the alkyl group may be substituted with hydroxyl group, carboxyl group, amino group, methylthio group, mercapto group, guanidyl group, imidazolyl group or benzyl group), and R1and R2represent each independently hydrogen atom, alkyl group, aralkyl group, cycloalkyl group or aryl group;R represents hydrogen atom, alkyl group, aralkyl group, cycloalkyl group, aryl group, monovalent metal, amine or ammonium; and the symbol ‘*’ represents a position of an asymmetric carbon atom. The above-mentioned compounds can be prepared by condensing tryptophan with a stereoisomeric α-amino acid or carboxylic acid to form an amide form and subjecting or carboxylic acid to form an amide form and subjecting the amide form to oxidative cyclization to form an oxazole ring at once. The compounds exhibit; physiological activities such as inhibitory action against lipid peroxidation, and can be therefore utilized in the form of lipid peroxidation inhibitors containing the same as the active ingredient.
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Page column 10
(2010/11/30)
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- Total synthesis of zaragozic acid A (squalestatin S1). Degradation to a relay compound and reassembly of the natural product
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Zaragozic acid A (squalestatin S1) (1) was converted into the simpler derivative 2, which was reconverted into the natural product, thus establishing 2 as a viable relay compound for total synthesis of 1. The degradation consisted of formation of the tri-tert-butyl ester (3), from which the two side chains were sequentially removed to obtain 8. Aldehyde 8 was converted into dimethyl acetal 2 in standard fashion. The C6 acyl side chain 14 was prepared from (S)-2-methylbutanol ('active amyl alcohol'), and the desired 4S configuration was obtained by use of Evans asymmetric enolate methylation. The C1 alkyl side chain was prepared as stannane 23a from (R)-2-methyl-3-phenylpropanol (21). For conversion of 2 back into zaragozic acid A, the dimethyl acetal was first converted into the cyclic acetal 17, thus protecting the C7 hydroxyl group. The remaining hydroxyl group was then acylated with acid 14 to obtain 18, which was transformed into aldehyde 20. The C1 alkyl chain was elaborated by the addition of a chiral α-alkoxyorganocerium reagent, obtained from 23a, to aldehyde 20. The resulting mixture of diastereomeric secondary alcohols was converted into zaragozic acid A (1) in six steps.
- Stoermer, Doris,Caron, Stephane,Heathcock, Clayton H.
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p. 9115 - 9125
(2007/10/03)
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- Pheromone Synthesis, CLXXVI: Synthesis of the four stereoisomers of 3,13-dimethylheptadecane, the major sex pheromone component of the western false hemlock looper
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All of the four stereoisomers of 3,13-dimethylheptadecane (1), the female-produced sex pheromone of the western false hemlock looper (Nepytia freemani), were synthesized by starting from the enantiomers of citronellol (2a) and 2-methyl-1-butanol (4a). VCH Verlagsgesellschaft mbH, 1996.
- Takikawa, Hirosato,Shirai, Yasuo,Kobayashi, Makoto,Mori, Kenji
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p. 1965 - 1970
(2007/10/03)
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- Pheromones 80. Synthesis of (S)-(+)-manicone and (S)-(+)-normanicone, mandibular gland constituents of myrmicine ants
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Optically active (4E,6S)-(+)-4,6-dimethyloct-4-en-3-one (10a), manicone, and (3E,5S)-(+)-3,5-dimethylhept-3-en-2-one (10b), normanicone, the biologically active stereoisomers of mandibular gland alarm pheromone components of Manica ants, were synthesized by three different routes starting from (S)-(-)-2-methyl-butan-1-ol (1).
- Martischonok,Melikyan,Mineif,Vostrowsky,Bestmann
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p. 560 - 564
(2007/10/02)
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- Chemistry of Oxaziridines. 15. Asymmetric Oxidations Using 3-Substituted 1,2-Benzisothiazole 1,1-Dioxide Oxides
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The synthesis and asymmetric oxidations of chiral nonracemic 3-substituted 1,2-benzisothiazole 1,1-dioxide oxides (6) are described.These new N-sulfonyloxaziridines are prepared by oxidation of the corresponding enantiomerically pure sulfonimines 5.These reagents oxidize sulfides to sulfoxides (11-52percent ee), epoxidize nonfunctionalized alkenes (17-61percent ee), and oxidize enolates to α-hydroxy carbonyl compounds (11-81percent ee).Epoxidation of (-)-(S)-limonene with (+)-(2R,3S)-6a, a double asymmetric synthesis, affords a 93:7 cis/trans mixture of limonene oxides.Evaluation ofpossible transition-state structures suggests that the molecular recognition is primarily determined by steric factors.These reagents are less effective than N-sulfonyloxaziridines 1-3 in their asymmetric oxidations because they lack well-defined regions that are topologically dissimilar near the active site.
- Davis, Franklin A.,ThimmaReddy, R.,McCauley, John P.,Przeslawski, Robert M.,Harakal, Mark E.,Carroll, Patrick J.
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p. 809 - 815
(2007/10/02)
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- Pheromone Synthesis, CXXV. Synthesis of the Four Possible Stereoisomers of 3,7-Dimethylnonadecane, the Female Sex Pheromone of Agromyza frontella Rondani
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The synthesis of the four possible stereoisomers of 3,7-dimethylnonadecane (1) has been achieved by starting from the enantiomers of methyl 3-hydroxy-2-methylpropanoate (2) and (R)-(+)-citronellic acid (3).
- Mori, Kenji,Wu, Jiang
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p. 213 - 217
(2007/10/02)
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- Synthesis of the lipophilic side chain of the cyclic hexadepsipeptide antibiotic L-156,602
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The 14-carbon tetrahydropyranylpropionic acid side chain of the cyclic hexadepsipeptide antibiotic L-156,602 (1) has been prepared as the methyl ester derivative 5. Asymmetric synthesis of the key intermediate 11-carbon lactone 7 was accomplished using diastereoselective alkylation of the alkoxide enolate of methyl (R)-3-hydroxybutanoate. A second route to lactone 7 utilized sequential organometallic reactions of the pinanediol boronic ester 17 to control two chiral centers. The enolate of the chiral dioxolanone 6 condensed with lactone 7 to produce the complete 14-carbon skeleton as a single diastereomer.
- Caldwell,Rupprecht,Bondy,Davis
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p. 2355 - 2361
(2007/10/02)
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- Pheromones, 65. - Identification of the Volatile Components of the Mandibular Gland Secretion of the Ant Manica rubida: Structure Elucidation, Synthesis, and Absolute Configuration of Manicone
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By means of gas chromatography and mass spectrometry, manicone, (4E)-4,6-dimethyl-4-octen-3-one (1), was identified as the main component of the mandibular gland secretion of the ant Manica rubida.In addition the presence of homomanicone (2), bishomomanicone (3), normanicone (7), and a few aliphatic aldehydes and ketones was also evident in the gland.Racemic 1, 2, and 7 and optically active dihydromanicone (4), were synthesized.The (S) configuration of 1 was determined by complexation gas chromatography, on a chiral phase, of 4 as well as of the hydrogenation products of racemic and natural 1.
- Bestmann, Hans Juergen,Attygalle, Athula B.,Glasbrenner, Juergen,Riemer, Roland,Vostrowsky, Otto,et al.
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- Diastereoselective Synthesis of Nitroaldol Derivatives
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Three methods are described by which diastereomerically enriched nitroaldols and their O-silylated derivatives can be prepared. threo-Nitroaldols prevail up to 10:1 over the erythro-isomers if doubly deprotonated nitroaldols 28 are quenched with acetic acid (THF/HMPT or DMPU, -100 deg C) (see Scheme 5 and Table 2).O-Trimethyl- or O-(t-butyl)dimethylsilylated (TBDMSi) erythro-nitroaldols can be obtained by protonation of the corresponding lithium nitronates (35, 39) in THF at low temperature (see Schemes 6 and 7).The erythro-O-TBDMSi-nitroaldol derivatives are also formed in the fluoride catalyzed addition of TBDMSi-nitronates (40-45) to aldehydes (see Schemes 8 and 9).In the latter reaction no 1,2-asymmetric induction is observed if α-branched silylnitronates or aldehydes are employed (see 48/49 and 50/51). - The stereochemical course of the reactions leading to erythro-O-TBDMSi-nitroaldols follows topological rules of broad applicability (see Scheme 10); possible mechanisms are discussed.- The configuration of erythro/threo-nitroaldols is determined by chemical correlation (see 24-26) and by 13C-NMR. spectroscopy. - Some examples of the preparation of diastereomerically enriched 1,2-aminoalcohols by reduction of the corresponding nitro compounds without loss of configurational purity are described (see Schemes 11 and 12).
- Seebach, Dieter,Beck, Albert K.,Mukhopadhyay, Triptikumar,Thomas, Elizabeth
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p. 1101 - 1133
(2007/10/02)
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