- Novel protection of 1,2-diol for trans-dihydroxycyclopentene ring construction by the C[sbnd]H insertion of alkylidene carbene: Formal total synthesis of (+)-trehazolin
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The chiral vicinal diol was protected as 6-methylene-1,4-dioxepane to construct a cyclopentene ring by the C[sbnd]H insertion of alkylidene carbene. The removal of the protecting group was achieved in a few steps, affording the corresponding diol in a reasonable yield. Using these reactions, the known synthetic intermediate for (+)-trehazolin was synthesized from D-diethyl tartrate. In addition, a short route to the intermediate from a D-mannitol derivative was described.
- Ohira, Susumu,Kuboki, Atsuhito,Takimoto, Yoshimi,Matsuda, Kyosuke,Itasaki, Saori,Urushibata, Yuki,Takano, Yoshiyuki,Nakamura, Yuuki
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- Hydrogen Bonding-Assisted Enhancement of the Reaction Rate and Selectivity in the Kinetic Resolution of d,l-1,2-Diols with Chiral Nucleophilic Catalysts
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An extremely efficient acylative kinetic resolution of d,l-1,2-diols in the presence of only 0.5 mol% of binaphthyl-based chiral N,N-4-dimethylaminopyridine was developed (selectivity factor of up to 180). Several key experiments revealed that hydrogen bonding between the tert-alcohol unit(s) of the catalyst and the 1,2-diol unit of the substrate is critical for accelerating the rate of monoacylation and achieving high enantioselectivity. This catalytic system can be applied to a wide range of substrates involving racemic acyclic and cyclic 1,2-diols with high selectivity factors. The kinetic resolution of d,l-hydrobenzoin and trans-1,2-cyclohexanediol on a multigram scale (10 g) also proceeded with high selectivity and under moderate reaction conditions: (i) very low catalyst loading (0.1 mol%); (ii) an easily achievable low reaction temperature (0 °C); (iii) high substrate concentration (1.0 M); and (iv) short reaction time (30 min). (Figure presented.).
- Fujii, Kazuki,Mitsudo, Koichi,Mandai, Hiroki,Suga, Seiji
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supporting information
p. 2778 - 2788
(2017/08/23)
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- An optimized synthetic route for the preparation of the versatile chiral building block 1,4-di-O-benzylthreitol
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An improved five-step procedure has been applied to synthesize enantiopure l- and d-1,4-di-O-benzylthreitol out of readily available l- and d-tartaric acid. Through the use of modern reagents and enhanced work-up conditions these useful auxiliaries were o
- Meier, Bettina,Kollroser, Manfred,Presser, Armin
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p. 305 - 309
(2014/03/21)
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- Synthesis of chiral 18-crown-6 ethers containing lipophilic chains and their enantiomeric recognition of chiral ammonium picrates
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Four new chiral 18-crown-6 ethers have been prepared to be used in enantiomeric recognition and extraction. The influence of the lipophilic character and bulkiness of the substituents on the complexation of different chiral ammonium picrates in CD3CN has been evaluated. Racemic aqueous solutions of the ammonium salts have been enriched in one enantiomer after extraction experiments, and the enantiomeric excesses have been calculated.
- Colera, Manuel,Costero, Ana M.,Gavina, Pablo,Gil, Salvador
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p. 2673 - 2679
(2007/10/03)
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- Enanthioselective Phase-Transfer Catalysis by Optically Active Crown Ethers
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1,2-Bis(hydroxymethyl)-15-crown-5 (1a), its dibenzyl ether (1b), and a series of esters with substituted benzoic acid (3) were probed as enanthioselective phase-transfer catalysts.Optical yields were observed in epoxidations of unsaturated ketones by hypochlorite and in cyanide additions to such compounds.The maximum ee value was 45percent.Polar side groups of the optically active crown ethers proved to be vital for enanthiomeric excesses.
- Dehmlow, Eckehard V.,Sauerbier, Christiane
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p. 181 - 186
(2007/10/02)
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- Homochiral Ketals in Organic Synthesis. Enantioselective Synthesis of (R)-Muscone
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An efficient, enantioselective preparation of (R)-muscone employing a diastereoselective Simmons-Smith cyclopropanation is described.Cyclopropanation is directed via chelation control by a homochiral ketal protecting group derived from unnatural tartaric acid.The overall yield of (R)-muscone (>95percent R) from commercially available cyclopentadecanone is 60percent over seven steps.
- Nelson, Keith A.,Mash, Eugene A.
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p. 2721 - 2724
(2007/10/02)
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