- Enzymatic resolution by CALB of organofluorine compounds under conventional condition and microwave irradiation
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Enzymatic kinetic resolution of organofluorine rac-alcohols by CALB yielded ( )-(R)-2,2,2-trifluoro-1- phenylethanol (2a), ()-(R)-1-(3-bromophenyl)-2,2,2- trifluoroethanol (2b), ()-(R)-1-(4-bromophenyl)- 2,2,2-trifluoroethanol (2c), ()-(S)-1-(2,4,5-trifluorophenyl)ethanol (2d), (+)-(S)-2,2,2-trifluoro-1- phenylethyl acetate (3a), (+)-(S)-1-(3-bromophenyl)-2,2,2-trifluoroethyl acetate (3b), (+)-(S)-1-(4- bromophenyl)-2,2,2-trifluoroethyl acetate (3c) and (+)-(R)-1-(2,4,5-trifluorophenyl)ethyl acetate (3d) in high enantiomeric excess (up to >99% ee). The reactions were conducted under conventional conditions (orbital shaking) and microwave irradiation in toluene and vinyl acetate as acylating agent. The CALB showed excellent selectivities and good yields in the transesterification of fluorinated aromatic compounds.
- Ribeiro, Sandra S.,Raminelli, Cristiano,Porto, André L.M.
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- Lipase-catalyzed Irreversible Transesterification of Secondary Alcohols Using Isopropenyl Acetate
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Asymmetric acetylation of a set of secondary alcohols with the innocuous acyl donor isopropenyl acetate catalyzed by a lipase from Pseudomonas cepacia immobilized on ceramic particles (PSL-C) in toluene as organic medium afforded the chiral alcohols and the corresponding acetates in high enantiomeric excess (up to 99%). An effective baseline separation of the enantiomers of both substrate and product was performed in one analysis without derivatization using gas chromatography on a new chiral stationary phase (CSP) Chirasil-β-Dex containing an undecamethylene spacer (C11-Chirasil-Dex).
- Ghanem, Ashraf,Schurig, Volker
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p. 1151 - 1157
(2007/10/03)
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- Entrapment of Pseudomonas cepacia lipase with peracetylated β-cyclodextrin in sol-gel: Application to the kinetic resolution of secondary alcohols
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Co-lyophilized Pseudomonas cepacia lipase with peracetylated β-cyclodextrin was immobilized by the sol-gel process. The gel-entrapped lipase/cyclodextrin was prepared by the hydrolysis of methyltrimethoxysilane (MTMS) in the presence of the co-lyophilized lipase with peracetylated β-cyclodextrin prepared with different weight ratios (enzyme to CD). This type of enzyme preparation was subsequently used in the kinetic resolution of a set of secondary alcohols using isopropenyl acetate as an innocuous acyl donor in toluene as the organic medium. The resulting chiral alcohols (substrate) and the corresponding acetates (product) were baseline separated in one analysis without derivatization using gas chromatography on a new chiral stationary phase (CSP) Chirasil-β-Dex containing an undecamethylene spacer (C11-Chirasil-Dex).
- Ghanem, Ashraf,Schurig, Volker
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p. 2547 - 2555
(2007/10/03)
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- Alkylnickel and -palladium alkoxides associated with alcohols through hydrogen bonding
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trans-PdR2L2(R = CH3, C2H5; L = PMe3, PEt3) and trans-NiMe2(PMe3)2 react with 2 equiv of fluorinated alcohols and para-substituted phenols to give complexes formulated as trans-PdR(OR′)(HOR′)L2 (R′ = CH(CF3)Ph, C6H5, p-CH3C6H4, p-CH3OC6H4, p-ClC6H4, P-BrC6H4, p-FC6H4) and trans-NiMe(OR′)(HOR′)(PMe3)2 (R′ = CH(CF3)Ph, C6H5), respectively. IR and NMR spectra of these complexes indicate the presence of strong O-H?O hydrogen bonding between the alkoxide (or aryloxide) ligand and the alcohol (or substituted and nonsubstituted phenol) both in the solid state and in solution. X-ray crystallography of trans-PdMe(OPh)(HOPh)(PMe3)2 and trans-NiMe(OPh)(HOPh)(PMe3)2 shows that the phenoxide oxygen in each complex is associated with phenol through hydrogen bonding. Reactions of trans-PdMe2(PMe3)2 with equimolar substituted and nonsubstituted phenols, respectively, give trans-PdMe(OC6H4-p-X)(PMe3)2 (X = H, Me, OMe, F, Cl, Br), which react with additional equimolar phenols to give phenol-bonded palladium complexes trans-PdMe(OC6H4-p-X)(HOC6H 4-p-X)(PMe3)2. trans-PdMe(OPh)(PMe3)2 reacts also with fluorinated alcohols to give trans-PdMe(OPh)(HOCH(CF3)Ph)(PMe3)2 and trans-PdMe(OPh)(HOCH(CF3)2)(PMe3)2, which are fully characterized by means of IR and NMR spectroscopy and X-ray crystallography. 1H NMR spectra of mixtures of phenol with cis-PdMe2(dmpe) (dmpe = 1,2-bis(dimethylphosphino)ethane) and cis-PdMe2(dpe) (dpe = 1,2-bis(diphenylphosphino)ethane) indicate formation of strong O-H?O hydrogen bonding between phenol and the phenoxide ligand in solution. Equilibrium constants for the association of phenol with the palladium phenoxide having dmpe ligand, obtained by means of 1H NMR spectroscopy, are smaller than those of trans-PdMe(OPh)(PMe3)2 with phenol. NMR spectra of trans-PdMe(OCH(CF3)Ph)(HOCH(CF3)Ph)(PMe3) 2 and trans-PdMe(OAr)(HOAr)(PMe3)2 at variable temperatures (-60 to +40 °C) indicate the presence of intramolecular alkoxide-exchange process between the alkoxide ligand and the alcohol moiety on the NMR time scale. Addition of phenol to trans-PdMe(OCH(CF3)Ph)(HOCH(CF3)Ph)(PMe3) 2 causes displacement of the alkoxide ligand by phenoxide group to give trans-PdMe(OPh)(HOCH(CF3)Ph)(PMe3)2. Reactions of trans-PdMe(OCH(CF3)Ph)(HOCH(CF3)Ph)(PMe3) 2 and trans-PdMe(OPh)(HOCH(CF3)Ph)(PMe3)2 with CO give MeCOOCH(CF3)Ph in 99% and 46% yields, respectively. Reactions of trans-PdMe(OCH(CF3)Ph)(HOCH(CF3)Ph)(PMe3) 2 with aryl esters give methylpalladium aryloxide complexes and esters of the fluorinated alcohol through exchange of the alkoxide group between the complex and the ester. The alkoxide (phenoxide) complexes catalyze transesterification of alcohols with esters. Mechanistic implications of the present results regarding the transesterification are presented.
- Kim, Yong-Joo,Osakada, Kohtaro,Takenaka, Akio,Yamamoto, Akio
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p. 1096 - 1104
(2007/10/02)
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- Solvolysis of 1-Aryl-2,2,2-trifluoroethyl Sulfonates. Kinetic and Stereochemical Effects in the Generation of Highly Electron-Deficient Carbocations
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Solvolysis rates of sulfonates XC6H4CH(O3SR)CF3 (R = p-Tol or CF3) correlate with ?+(X) with values of ρ+ between -6.7 and -11.9 depending upon solvent.For the tosylates the rates depend on the solvent parameter YOTs with
- Allen, Annette D.,Ambidge, I. Christopher,Che, Claudius,Micheal, Hany,Muir, Ronald J.,Tidwell, Thomas T.
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p. 2343 - 2350
(2007/10/02)
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