- Enantioselective cross-coupling of meso -epoxides with aryl halides
-
The first enantioselective cross-electrophile coupling of aryl bromides with meso-epoxides to form trans-β-arylcycloalkanols is presented. The reaction is catalyzed by a combination of (bpy)NiCl2 and a chiral titanocene under reducing conditions. Yields range from 57 to 99% with 78-95% enantiomeric excess. The 30 examples include a variety of functional groups (ether, ester, ketone, nitrile, ketal, trifluoromethyl, sulfonamide, sulfonate ester), both aryl and vinyl halides, and five- to seven-membered rings. The intermediacy of a carbon radical is strongly suggested by the conversion of cyclooctene monoxide to an aryl [3.3.0]bicyclooctanol.
- Zhao, Yang,Weix, Daniel J.
-
supporting information
p. 3327 - 3340
(2015/03/30)
-
- Direct observation of enantiomer discrimination of epoxides by chiral salen complexes using ENDOR
-
Electron nuclear double resonance (ENDOR) spectroscopy was used to investigate the weak enantioselective binding between chiral salen complexes [VO(1)] ((R,R)- and (S,S)-vanadyl N,N-bis(3,5-di-tert-butylsalcylidene)-1,2-cyclohexanediamine) and chiral epoxides (e.g., (R)-/(S)-propylene epoxide, 5) in frozen (10 K) solution. Differences in epoxide binding by enatiomers of [VO(1)] was evidenced by changes to the 1H epoxide derived peaks in the ENDOR spectra, such that (R,R)-[VO(1)] + (R)-5 and (R,R)-[VO(1)] + (S)-5 yield noticeably different spectra. These changes were assigned to the small structural differences between the diastereomeric metal-epoxide adducts. Simulation of the spectra revealed differences in the VO...1Hepoxide distances for the diastereomeric pairs, which was confirmed by a complementary set of density functional theory (DFT) calculations. While the epoxide molecule is very weakly coordinated, ENDOR measurements of the racemic complex in racemic epoxide nevertheless indicated the preferential coordination of the (R)-5 to (R,R)-[VO(1)] (likewise (S)-(5) to (S,S)-[VO(1)]), which is favored over the binding of (S)-5 epoxide to (R,R)-[VO(1)] (and likewise (R)-5 epoxide to (S,S)-[VO(1)]). This demonstrates the unique power of the ENDOR technique to resolve weak chiral interactions for which EPR spectroscopy alone lacks sufficient resolution. Copyright
- Fallis, Ian A.,Murphy, Damien M.,Willock, David J.,Tucker, Richard J.,Farley, Robert D.,Jenkins, Robert,Strevens, Robert R.
-
p. 15660 - 15661
(2007/10/03)
-
- Stereoinversion of arylethanols by Geotrichum candidum
-
Aromatic and aliphatic racemic alcohols were converted to the corresponding optically active alcohols in high yield with excellent enantioselectivities by the use of Geotrichum candidum IFO 5767.
- Nakamura, Kaoru,Fujii, Mikio,Ida, Yoshiteru
-
p. 3147 - 3153
(2007/10/03)
-
- Humicola lanuginosa lipase-catalyzed enantioselective resolution of β-hydroxy sulfides: Versatile synthons for enantiopure β-hydroxy sulfoxides
-
Humicola lanuginosa lipase-catalyzed acylation of β-hydroxy sulfides provides both the (R)- and (S)-enantiomers in high enantiomeric purity. In two cases the resolved hydroxy sulfides were oxidized to give β-hydroxy sulfoxides in >99% e.e. The effect of substituents on enantioselectivity is discussed.
- Singh, Satwinder,Kumar, Subodh,Chimni, Swapandeep Singh
-
p. 2457 - 2462
(2007/10/03)
-
- Asymmetric reduction of ketones by Geotrichum candidum in the presence of Amberlite Xad, A solid organic solvent
-
Asymmetric reduction of ketones by Geotrichum candidum in the presence of Amberlite XAD, a solid organic solvent, was described. A hydrophobic polymer, XAD, was used as material to control the stereochemical course of microbial reductions. Aliphatic and aromatic ketones were reduced to the corresponding (S)-alcohols in excellent enantiomeric excess (ee) in the presence of XRD while low enantioselectivities were observed in the absence of the polymer.
- Nakamura, Kaoru,Fujii, Mikio,Ida, Yoshiteru
-
p. 3205 - 3211
(2007/10/03)
-
- Novel bi- and tridentate phosphane and thioether ligands derived from chiral α-hydroxy acids
-
Novel bi- and tridentate ligands with phosphane and thioether moieties have been prepared in enantiomerically pure form in good to excellent yields by substitution reactions with phosphorus and sulfur nucleophiles of easily available tosylates derived from natural chiral α-hydroxy acids.
- Christoffers, Jens,Roessler, Ulrich
-
p. 1207 - 1215
(2007/10/03)
-
- Highly Regioselective and Stereospecific Functionalization of 1,2-Proanediol with Trimethyl(X)silanes Employing the 1,3,2λ5-Dioxaphospholane Methodology
-
The regioselective ring opening of (S)-4-methyl-2,2,2-triphenyl-1,3,2λ5-dioxaphospholanes (2) was initiated with several trimethylsilyl reagents (Me3SiX: X = PhS, I, Br; Cl, CN, and N3) to afford the regioisomeric (silyloxy)phosphonium salts.A stereospecific extrusion of triphenylphosphine oxide from these oxyphosphonium salts gave predominatly the thermodynamically less stable C-2-X-substituted derivatives with nearly complete inversion of stereochemistry at the C-2 stereogenic center (i.e., X = PhS).
- Mathieu-Pelta, Isabel,Evans, Slayton A.
-
p. 3409 - 3413
(2007/10/02)
-
- A Facile Chemoenzymatic Route to Enantiomerically Pure Oxiranes: Building Blocks for Biologically Active Compounds
-
The enantiomerically pure building blocks (R)- and (S)-1-4 were prepared both by enantioselective, enzymatic hydrolysis and by acyl transfer, and subsequently converted into the corresponding enantiomerically pure oxiranes (R)-and (S)-7 and 8.
- Goergens, Ulrich,Schneider, Manfred P.
-
p. 1064 - 1066
(2007/10/02)
-
- Switching of the Direction of Enzyme-Mediated Oxidation and Reduction of Sulfur-Substituted 2-Propanols and 2-Propanones
-
Incubation of 1-(phenylsulfenyl)-2-propanone with Corynebacterium equi IFO 3730 grown on hexadecane at pH 6.5 afforded the corresponding 1-substituted S propanols. 1-(Phenylsulfinyl)-2-propanone was also reduced by the microorganism, the product being aff
- Ohta, Hiromichi,Kato, Yasuo,Tsuchihashi, Gen-ichi
-
p. 2735 - 2739
(2007/10/02)
-
- pH DEPENDENT OXIDATION-REDUCTION OF 1-BENZENESULFENYL-2-PROPANONE AND ITS OXIDES BY A MICROORGANISM
-
Incubation of 1-benzenesulfenyl-2-propanone with Corynebacterium equi IFO 3730 in a weakly acidic medium afforded (S)-1-benzenesulfenyl-2-propanol.On the contrary, when the cultivation was carried out at pH 8 with the same bacterium, only the (S)-alcohol
- Ohta, Hiromichi,Kato, Yasuo,Tsuchihashi, Gen-ichi
-
p. 581 - 584
(2007/10/02)
-