- A chemo-enzymatic route to diastereoisomers of 2-methyl-1-phenyl-1,3-butanediol: the dual role of microorganisms
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Diastereoisomers (1S,2R,3S)-, (1R,2R,3S)-, (1R,2S,3S)- and (1S,2S,3S)-2-methyl-1-phenyl-1,3-butanediols were prepared by simple and convenient strategies using two different chemo-enzymatic approaches for the reduction of racemic 2-methyl-1-phenyl-1,3-but
- Ahmad,Taneja,Singh,Anand,Qurishi,Koul,Qazi
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p. 445 - 450
(2007/10/03)
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- Synthesis of valuable chiral intermediates by isolated ketoreductases: Application in the synthesis of α-alkyl-β-hydroxy ketones and 1,3-diols
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Regio- and stereoselective reductions of α-substituted 1,3-diketones to the corresponding β-keto alcohols or 1,3-diols by using commercially available ketoreductases (KREDs) are described. A number of α-monoalkyl- or dialkyl-substituted symmetrical as well as non-symmetrical diketones were reduced in high optical purities and chemical yields, in one or two enzymatic reduction steps. In most cases, two or even three out of the four possible diastereomers of α-alkyl-β-keto alcohols were synthesized by using different enzymes, and in two examples both ketones were reduced to the 1,3-diol. By replacing the α-alkyl substituent with the OAc group, 1-keto-2,3-diols, as well as 1,2,3-triols were synthesized in high optical purities. These enzymatic reactions provide a simple, highly stereoselective and quantitative method for the synthesis of different diastereomers of valuable chiral synthons from non-chiral, easily accessible 1,3-diketones.
- Kalaitzakis, Dimitris,Rozzell, J. David,Smonou, Ioulia,Kambourakis, Spiros
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p. 1958 - 1969
(2007/10/03)
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- Synthesis of (+)-conagenin
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An efficient total synthesis of (+)-conagenin was achieved. The right fragment of conagenin, α-methylserine containing a quaternary stereocenter attached to nitrogen, was synthesized using allyl cyanate-to-isocyanate rearrangement. The left fragment, 2,4-
- Matsukawa, Yohei,Isobe, Minoru,Kotsuki, Hiyoshizo,Ichikawa, Yoshiyasu
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p. 5339 - 5341
(2011/11/14)
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- Reexamination of CeCl3 and InCl3 as activators in the diastereoselective mukaiyama aldol reaction in aqueous media
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A search for suitable reaction conditions in Mukaiyama-type aldol condensations activated by CeCl3 and InCl3 revealed that the reaction proceeds best in i-PrOH/ H2O (95:5). Contrary to literature precedent, no reaction was
- Munoz-Muniz, Omar,Quintanar-Audelo, Martina,Juaristi, Eusebio
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p. 1622 - 1625
(2007/10/03)
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- Rare Earth Metal Complexes as Water-Tolerant Lewis Acid Catalysts in Organic Synthesis
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Rare earth metal triflates are stable in aqueous media and can act as Lewis acid catalysts in several carbon-carbon bond forming reactions. This article describes some of these reactions; aldol and Mannich-type reactions in aqueous solution, and Friedel-Crafts acylations and Fries rearrangement in organic solvents. The reactions proceeded smoothly in the presence of a catalytic amount of the triflate under mild conditions. Moreover, the catalysts could be recovered after the reactions were completed and could be reused.
- Kobayashi,Hashiya,Ishitani,Moriwaki,Nagayama
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p. 193 - 202
(2007/10/03)
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- Lanthanide Triflates as Water-Tolerant Lewis Acids. Activation of Commercial Formaldehyde Solution and Use in the Aldol Reaction of Silyl Enol Ethers with Aldehydes in Aqueous Media
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Lanthanide trifluoromethanesulfonates (triflates), especially ytterbium triflate (Yb(OTf)3), were found to be stable Lewis acids in water.In the presence of a catalytic amount of lanthanide triflate, formaldehyde in water solution (commercial formaldehyde
- Kobayashi, Shu,Hachiya, Iwao
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p. 3590 - 3596
(2007/10/02)
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- The aldol reaction of silyl enol ethers with aldehydes in aqueous media
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The aldol reaction of silyl enol ethers with aldehydes is successfully carried out in aqueous media by using a lanthanide trifluoromethanesulfonate as a catalyst. Water soluble aldehydes are applicable and the catalyst can be recovered and reused in this
- Kobayashi,Hachiya
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p. 1625 - 1628
(2007/10/02)
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- Meerwein-Ponndorf-Verley-Type Reduction of Dicarbonyl Compounds to Hydroxy Carbonyl Compounds and α,β-Unsaturated Carbonyl Compounds to Allylic Alcohols Catalyzed by Zirconocene and Hafnocene Complexes
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Group IVA metallocene complexes such as bis(η5-cyclopentadienyl)zirconium dihydrides, Cp2ZrH2 (1), and hafnium dihydrides, Cp2HfH2 (8), catalyze the chemoselective reduction of polycarbonyl compounds to hydroxy carbonyl compounds.For instance, the reduction of keto aldehydes 3-ketobutanal (2g) and 2-phenyl-2-ketoethanal (2h) proceeded selectively at aldehyde group to provide the corresponding hydroxy ketones 3g and 3h in 91percent and 93percent yields, respectively.Under similar conditions, however, cyclohexanediones were easily aromatized to benzenediols.On the other hand, 1 and 8 also catalyze the selective 1,2-reduction of various types of α,β-unsaturated carbonyl compounds, giving the corresponding allylic alcohols in good to excellent yields.Thus, steroidal dicarbonyl compounds, having an enone framework in their molecules Δ4-androstene-3,17-dione (11a) and Δ4-progestene-3,20-dione (11b) were reduced by 1 to 17-hydroxy-Δ4-androsten-3-one (12a) and 20-hydroxy-Δ4-progest-3-one (12b), which are essential human hormones, in 80percent and 67percent yields, respectively.
- Nakano, Tatsuya,Umano, Shigetoshi,Kino, Yoshio,Ishii, Yasutaka,Ogawa, Masaya
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p. 3752 - 3757
(2007/10/02)
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