1517-66-4Relevant academic research and scientific papers
Highly enantioselective reduction of prochiral ketones with N,N-diethylaniline·borane (DEANB) in oxazaborolidine-catalyzed reductions
Salunkhe, Ashok M.,Burkhardt, Elizabeth R.
, p. 1523 - 1526 (1997)
A variety of prochiral ketones including phenyl, aralkyl, cycloalkyl, alkyl and tertiary alkyl are enantioselectively reduced with an oxazaborolidine catalyst (5 mol% of the Me-CBS) and N,N-diethylaniline·borane as the borane source. The enantioselectivity of the reduction produced secondary alcohols in the range of 90 to ≤99% ee.
Enantioselective Borane Reduction of Ketones Catalysed by a Chiral Oxazaphospolidine-Borane Complex
Brunel, Jean-Michel,Pardigon, Olivier,Faure, Bruno,Buono, Gerard
, p. 287 - 288 (1992)
The chiral oxazaphospholidine-borane complex 2 was used as catalyst (2 mol percent) in asymmetric reduction of ketones by borane with an enantioselectivity ranging from 33 to 92percent at 110 deg C and 100percent conversion; under stoichiometric conditions the reduction proceeded with 99percent enantiomeric excess.
Addition Compounds of Alkali Metal Hydrides. 29. Preparation and Properties of Chiral Dialkylmonoalkoxyborohydrides. A New Class of Asymmetric Reducing Agents
Brown, Herbert C.,Park, Won Suh,Cho, Byung Tae
, p. 3278 - 3282 (1986)
A series of chiral 9-alkoxy-9-borabicyclononane derivatives were synthesized by the reaction of 9-borabicyclononane (9-BBN) with several readily available chiral alcohols, such as (-)-isopinocampheol, (+)-menthol, (-)-4-isocaranol, (+)-trans-2-methylcyclopentanol, and (-)-1,2:5,6-di-O-isopropylidene-α-D-glucofuranose.A chiral borinic ester possessing a cyclic chiral dialkylboryl moiety, (+)-2-(cyclohexyloxy)-4,8-dimethyl-2-borabicyclononane, was also synthesized.With one exception, all of these chiral borinic esters were readily converted into the corresponding chiral dialkylmonoalkoxy borohydrides by treatment with excess potassium hydride in THF at 25 deg C.The addition of potassium hydride to (+)-9-(menthyloxy)-9-borabicyclononane (9-O-Men-9-BBN) was very slow, requiring 15 days at 65 deg C (refluxing THF).The chiral dialkylmonoalkoxyborohydrides thus formed are all stable at 25 deg C and can be stored for several months.They were tested against acetophenone and 3-methyl-2-butanone as representative prochiral ketones.These reagents reduce acetophenone with up to 78percent ee and 3-methyl-2-butanone with up to 61percent ee at -78 deg C.
Use of new chiral tricoordinated phosphorus borane complexes in enantioselective borane reduction of ketones: Complexes structure and mechanistic studies
Brunel, Jean-Michel,Chiodi, Olivier,Faure, Bruno,Fotiadu, Frederic,Buono, Gerard
, p. 285 - 294 (1997)
New tricoordinated phosphorus borane complexes were synthesized and their use as catalysts in enantioselective borane reduction of prochiral aromatic and aliphatic ketones was investigated. The structure of (2K,5S)-2-o-anisyl-3-oxa-1-aza phosphabicyclo[3.3.0]octane-borane complex 1b and (2R,5S)-2,3-diphenyl-1,3-diazaphosphabicyclo[3.3.0]octane-borane complex 6a was established by X-ray diffraction analysis. A relationship has been established between the structure of the oxazaphospholidine borane complexes and the enantioselectivity obtained in the reduction of acetophenone, both with 2mol% and one equivalent of the catalyst. Among the different oxazaphospholidine borane complexes tested, only the complexes 1-3, including 3-oxa-1-azaphosphabicyclo-[3.3.0]octane and 3-oxa-1-azaphosphabicyclo[4.3.0]nonane moieties, were efficient catalysts. A rational mechanism is proposed according to the experimental results, especially from a deuterium labelling study.
Chiral borate esters in asymmetric synthesis: Part 2 - Asymmetric borane reduction of prochiral ketones in the presence of a chiral spiroborate ester
Liu, Dejun,Shan, Zixing,Zhou, Yan,Wu, Xiaojun,Qin, Jingui
, p. 2310 - 2317 (2004)
Asymmetric catalytic activity of the chiral spiroborate esters 1-9 with a O3BN framework (see Fig. 1) toward borane reduction of prochiral ketones was examined. In the presence of 0.1 equiv. of a chiral spiroborate ester, prochiral ketones were reduced by 0.6 equiv. of borane in THF to give (R)-secondary alcohols in up to 92% ee and 98% isolated yields (Scheme 1). The stereoselectivity of the reductions depends on the constituents of the chiral spiroborate ester (Table 2) and the structure of the prochiral ketones (Table 1). The configuration of the products is independent of the chirality of the diol-derived parts of the catalysts. A mechanism for the catalytic behavior of the chiral spiroborate esters (R,S)-2 and (S,S)-2 during the reduction is also suggested.
Diastereoselective Synthesis of P-Chirogenic and Atropisomeric 2,2′-Bisphosphino-1,1′-binaphthyls Enabled by Internal Phosphine Oxide Directing Groups
Huo, Shangfei,Li, Jianli,Wang, Tingyi,Wang, Zeming,Xue, Qingquan,Zhu, Meifang,Zuo, Weiwei
, p. 8153 - 8159 (2020)
Diphosphine ligands that merge both axial and P-centered chirality may exhibit superior or unique properties. Herein we report the diastereoselective introduction of P-centered chirality at the 2-position of the axially chiral 2′-(phosphine oxide)-1,1′-binaphthyl scaffold. A lithium–bromide exchange reaction of a 2-bromo-2′-(phosphine oxide)-1,1′-binaphthyl and treatment with dichlorophosphines followed by a nucleophilic organometallic reagent afforded unsymmetrical 2-phosphino-2′-(phosphine oxide)-1,1′-binaphthyls with binaphthyl axial chirality and one or two phosphorus stereocenters with a variety of P substituents. The final diastereomerically pure 2,2′-bisphosphino-1,1′-binaphthyls were obtained by reduction of the phosphine oxide directing group. Preliminary results demonstrated that a ligand with this hybrid chirality could induce higher stereoselectivity in the metal-complex-catalyzed asymmetric hydrogenation of a dialkyl ketone.
Discovery and Redesign of a Family VIII Carboxylesterase with High (S)-Selectivity toward Chiral sec-Alcohols
Park, Areum,Park, Seongsoon
, p. 2397 - 2402 (2022/02/17)
Highly enantioselective lipase has been widely utilized in the preparation of versatile enantiopure chiral sec-alcohols through kinetic or dynamic kinetic resolution. Lipase is intrinsically (R)-selective, and it is difficult to obtain (S)-selective lipase. Recent crystal structures of a family VIII carboxylesterase have revealed that the spatial array of its catalytic triad is the mirror image of that of lipase but with a catalytic triad that is distinct from lipase. We, therefore, hypothesized that the family VIII carboxylesterase may exhibit (S)-enantioselectivity toward sec-alcohols similar to (S)-selective serine protease, whose catalytic triad is also spatially arrayed as its mirror image. In this study, a homologous enzyme (carboxylesterase from Proteobacteria bacterium SG_bin9, PBE) of a known family VIII carboxylesterase (pdb code: 4IVK) was prepared, which showed not only moderate (S)-selectivity toward sec-alcohols such as 3-butyn-2-ol and 1-phenylethyl alcohol but also (R)-selectivity toward particular sec-alcohols among the substrates explored. Furthermore, the (S)-selectivity of PBE has been significantly improved by rational redesign based on molecular modeling. Molecular modeling identified a binding pocket composed of Ser381, Ala383, and Arg408 for the methyl substituent of (R)-1-phenylethyl acetate and suggested that larger residues may increase the enantioselectivity by interfering with the binding of the slow-reacting enantiomer. As predicted, substituting Ser381with larger residues (Phe, Tyr, and Trp) significantly improved the (S)-selectivity of PBE toward all sec-alcohols explored, even the substrates toward which the wild-type PBE exhibits (R)-selectivity. For instance, the enantioselectivity toward 3-butyn-2-ol and 1-phenylethyl alcohol was improved from E = 5.5 and 36.1 to E = 2001 and 882, respectively, by single mutagenesis (S381F).
A Cobalt(II) Complex Bearing the Amine(imine)diphosphine PN(H)NP Ligand for Asymmetric Transfer Hydrogenation of Ketones
Huo, Shangfei,Chen, Hong,Zuo, Weiwei
supporting information, p. 37 - 42 (2020/10/21)
Novel chiral cobalt complex a containing amine(imine)diphosphine PN(H)NP ligand and complex b containing bis(amine)diphosphine PN(H)N(H)P ligand were synthesized. The structures of two complexes were characterized by X-ray crystallography and high resolution mass spectrometry. The catalytic performances of cobalt complexes a and b for asymmetric transfer hydrogenation (ATH) of ketones under mild conditions were evaluated using 2-propanolisopropanol as solvent and hydrogen source after being activated by 8 equivalents of base. Complex a showed a good reactivity for reduction of ketones, with a turnover number (TON) of up to 555, and a maximum enantiomeric excess (ee) value of up to 91 %. Complex b exhibited inertness for hydrogenation of ketones. Electronic structure studies on a and b were conducted to account for the function of ligands on the catalytic performances.
London Dispersion Interactions Rather than Steric Hindrance Determine the Enantioselectivity of the Corey–Bakshi–Shibata Reduction
Eschmann, Christian,Song, Lijuan,Schreiner, Peter R.
, p. 4823 - 4832 (2021/02/01)
The well-known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
Boron containing chiral Schiff bases: Synthesis and catalytic activity in asymmetric transfer hydrogenation (ATH) of ketones
Pa?a, Salih,Arslan, Nevin,Meri??, Nermin,Kayan, Cezmi,Bingül, Murat,Durap, Feyyaz,Aydemir, Murat
, (2019/09/19)
Asymmetric Transfer Hydrogenation (ATH) has been an attractive way for the reduction of ketones to chiral alcohols. A great number of novel and valuable synthetic pathways have been achived by the combination usage of organometallic and coordination chemistry for the production of important class of compounds and particularly optically active molecules. For this aim, four boron containing Schiff bases were synthesized by the reaction of 4-formylphenylboronic acid with chiral amines. The boron containing structures have been found as stable compounds due to the presence of covalent B–O bonds and thus could be handled in laboratory environment. They were characterized by 1H NMR and FT-IR spectroscopy and elemental analysis and they were used as catalyst in the transfer hydrogenation of ketones to the related alcohol derivatives with high conversions (up to 99%) and low enantioselectivities (up to 22% ee).
