- Highly stereoselective syn-ring opening of enantiopure epoxides with nitric oxide
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Reaction of enantiopure epoxides (1) with NO occurred highly stereoselectively, affording syn-ring opened products, nitrates (2). The configuration of 2 was confirmed to be retained by determining the configuration of reduced products 1,2-glycols (4) from 2. A possible mechanism is suggested to trace out the syn-ring opening pathway.
- Wu, Wentao,Liu, Qiang,Shen, Yinglin,Li, Rui,Wu, Longmin
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- Oxidation of Alkenes with Aqueous Potassium Peroxymonosulfate and No Organic Solvent
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Aqueous potassium peroxymonosulfate oxidizes water-immiscible alkenes at room temperature in the absence of organic solvent.Acidic (pH 6.7 with NaHCO3 enabled selective epoxidations of 2,3-dimethyl-2-butene, 1-methylcyclohexene, cyclohexene, styrene, and β-methylstyrene.The order of decreasing reactivity of alkenes was: 2,3-dimethyl-2-butene > 1-methylcyclohexene cyclohexene > cyclooctene > α-methylstyrene β-methylstyrene > styrene > p-methylstyrene > allylbenzene. 1-Octene and tetrachloroethylene did not react.Phase-transfer catalysts, a colloidal cationic polymer, and a cationic surfactant microemulsion had little effect on the reaction.
- Zhu, Weiming,Ford, Warren T.
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- Stereospecific metabolic reduction of ketones
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The stereospecificity of the metabolic reduction of arylalkylketones was investigated. The ketones, propiophenone (I), phenylacetone (III), and 1-phenyl-1,2-propanedione (V) were reduced in vitro and in vivo in rats and rabbits to the corresponding alcohols, 1-phenyl-1-propanol (II), 1-phenyl-2-propanol (IV), and 1-phenyl-1,2-propanediol (VIII), respectively. For the analysis, a capillary GLC method employing chiral derivatizing reagents for the resolution the these optically active alcohols were utilized. This study revealed that the metabolic reduction of each ketone produced the corresponding alcohol as a mixture of its enantiomers. With one exception, the mixtures obtained from all in vivo and in vitro reactions were shown to contain at least 70% of one isomer [S(-)-II,S(+)-IV, and erythro-VIII, respectively, with in vitro reduction showing the highest degree of stereospecificity (90-98%). The in vivo reduction of I by the rat was exceptional in that both optical isomers of II were recovered in equal proportions.
- Prelusky,Coutts,Pasutto
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- Modular monodentate oxaphospholane ligands: Utility in highly efficient and enantioselective 1,4-diboration of 1,3-dienes
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Tune it up! Tunable, chiral, monodentate oxaphospholane ligands (termed OxaPhos) are highly effective in the Pt-catalyzed title reaction, providing the 1,4-addition products in enantiomer ratios approaching 99:1 (see scheme). In the presence of enantiomerically pure cis-iBu-OxaPhos, a catalyst loading of only 0.02 mol% [Pt(dba)3] was sufficient for effective reaction. pin=pinacolato, dba=dibenzylideneacetone.
- Schuster, Christopher H.,Li, Bo,Morken, James P.
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p. 7906 - 7909
(2011/10/09)
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- Hot water-promoted ring-opening of epoxides and aziridines by water and other nucleopliles
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Effective hydrolysis of epoxides and aziridines was conducted by heating them in water at 60 or 100 °C. Other types of nucleophile such as amines, sodium azide, and thiophenol could also efficiently open epoxides and aziridines in hot water. It was proposed that hot water acted as a modest acid catalyst, reactant, and solvent in the hydrolysis reactions.
- Wang, Zhi,Cui, Yong-Tao,Xu, Zhao-Bing,Qu, Jin
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p. 2270 - 2274
(2008/09/19)
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- Concatenated catalytic asymmetric allene diboration/allylation/ functionalization
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(Chemical Equation Presented) Palladium-catalyzed enantioselective diboration of prochiral allenes generates a reactive chiral allylboron intermediate which is a versatile reagent for the allylation of carbonyls. Experiments that improve the enantioselectivity of this process, examine the substrate scope, and are directed toward functionalization of the allylation intermediate are described.
- Woodward, Angela R.,Burks, Heather E.,Chan, Louis M.,Morken, James P.
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p. 5505 - 5507
(2007/10/03)
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- Hindered organoboron groups in organic chemistry. 23. The interactions of dimesitylboron stabilised carbanions with aromatic ketones and aldehydes to give alkenes
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Dimesitylboron stabilised carbanions react with diarylketones to give the corresponding alkenes in mild conditions with good yields. Reactions with aromatic aldehydes are more complex, but in all cases E-alkenes are available in good yields by trapping the intermediates with chlorotrimethylsilane followed by treatment with aq. HF/CH3CN. Treatment of the same intermediates with trifluoroacetic anhydride gives mainly the Z-alkenes. The design and mechanisms of these important processes are considered.
- Pelter,Buss,Colclough,Singaram
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p. 7077 - 7103
(2007/10/02)
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- Stereoselectrive Syntheses of Ephedrine and Related 2-Aminoalcohols of High Optical Purity from Protected Cyanohydrins
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Ephedrine and related optically active β-aminoalcohols can be prepared by zinc borohydride reduction of aryl O-protected magnesium imines and aryl α-hydroxyimimes which in turn are readily available from optically active cyanohydrins.
- Jackson, W. Roy,Jacobs, Howard A.,Matthews, Barry R.,Jayatilake, Gamini S.,Watson, Keith G.
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p. 1447 - 1450
(2007/10/02)
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- Synthesis of Optically Active 1-Phenyl-1,2-propanediol by Use of Baker's Yeast
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Reduction of 1-phenyl-1,2-propanedione with baker's yeast afforded (1R,2S)-1-phenyl-1,2-propanediol in high chemical and optical yield. (1R,2S)-, (1R,2R)- and (1S,2S)-1,2-propanediols were also prepared via (1R)- or (2S)-α-ketols, which were obtained as intermediates of the above reaction.
- Takeshita, Mitsuhiro,Sato, Takumi
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p. 1085 - 1086
(2007/10/02)
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- Asymmetric Synthesis of Both Enantiomers of Tomoxetine and Fluoxetine. Selective Reduction of 2,3-Epoxycinnamyl Alcohol with Red-Al.
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Both enantiomers of tomoxetine 7a,7b and fluoxetine 8a,8b (as their hydrochloride salts) have been synthetized from cinnamyl alkohol by asymmetric epoxidation, and their absolute configurations have been established.Optimal conditions for regioselective Red-Al reduction at C-2 of 2,3-epoxycinnamyl alcohol are discussed.
- Gao, Y.,Sharpless, K. B.
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p. 4081 - 4084
(2007/10/02)
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- THE DIMESITYLBORON GROUP IN ORGANIC SYNTHESIS 7. A UNIQUE VARIANT OF THE BORON-WITTIG REACTION WHICH STEREOSELECTIVELY YIELDS 1,2-DIOLS.
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Low temperature oxidation of the intermediates in the Wittig reactions of aryl aldehydes with carbanions stabilised with an adjacent dimesitylboron group leads stereoselectively to erythro-1,2-diols.The mechanistic implications for the boron-Wittig reactions are discussed.
- Pelter, Andrew,Buss, Dieter,Pitchford, Andrew
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p. 5093 - 5096
(2007/10/02)
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- Studies on the Autoxidation of cis- and trans-β-Methyl Styrene
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In the autoxidation of cis- and trans-β-methyl styrene at temperatures between 80 and 120 deg C the C=C-double bond is preferably attacked: 35-60percent of epoxides and their consecutive products and 25-50percent of benzaldehyde are obtained.Products of allylic oxidation are formed only with yields lower than 1percent; high-boiling or polymeric products, respectively, which could not be detected gaschromatographically are formed with yields lower than 20percent.The ratio of cis- to trans-epoxides in the case of cis-β-methyl styrene oxidation amounts to about 0.04, in the case of trans-β-methyl styrene oxidation this ratio is about 0.01.
- Fuchs, K. P.,Pritzkow, W.
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p. 353 - 361
(2007/10/02)
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