| 1. |
- Krajangsri, Suppachai, et al.
(author)
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Tandem Peterson olefination and chemoselective asymmetric hydrogenation of β-hydroxy silanes
- 2019
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In: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 10:12, s. 3649-3653
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Journal article (peer-reviewed)abstract
- Here, we report the first Ir-N,P complex catalyzed tandem Peterson olefination and asymmetric hydrogenation of -hydroxy silanes. This reaction resulted in the formation of chiral alkanes in high isolated yields (up to 99%) and excellent enantioselectivity (up to 99% ee) under mild conditions. Modification of the reaction conditions provides a choice to transform either an olefin or the -hydroxy silane in a chemoselective manner. Additionally, based on this method, an expedient enantioselective synthesis of (S)-(+)--curcumene, from a simple ketone, was accomplished in two steps with 75% overall yield and 95% ee.
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| 2. |
- Li, Jia-Qi, et al.
(author)
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Asymmetric Hydrogenation of Allylic Alcohols Using Ir-N,P-Complexes
- 2016
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 6:12, s. 8342-8349
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Journal article (peer-reviewed)abstract
- In this study, a series of gamma,gamma-disubstituted and beta,gamma-disubstituted allylic alcohols were prepared and successfully hydrogenated using suitable N,P-based Ir complexes. High yields and excellent enantioselectivities were obtained for most of the substrates studied. This investigation also revealed the effect of the acidity of the N,P-Ir-complexes on the acid sensitive allylic alcohols. DFT Delta pK(a) calculations were used to explain the effect of the N,P-ligand on the acidity of the corresponding Ir-complex. The selectivity model of the reaction was used to accurately predict the absolute configuration of the hydrogenated alcohols.
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| 3. |
- Liu, Jianguo, et al.
(author)
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Regioselective Iridium-Catalyzed Asymmetric Monohydrogenation of 1,4-Dienes
- 2017
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 139:41, s. 14470-14475
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Journal article (peer-reviewed)abstract
- A highly efficient regio- and enantioselective monohydrogenation of 1,4-dienes has been realized using an iridium catalyst with a chiral N,P-ligand under mild conditions. The substrate scope was studied and included both unfunctionalized as well as functionalized substituents on the meta- or para-position. Substrates having substituents with functionalities such as silyl protected alcohols or ketals were monohydrogenated in high regioselectivity and high enantiomeric excess (up to 98% ee).
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| 4. |
- Massaro, Luca, et al.
(author)
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Stereodivergent Synthesis of Trisubstituted Enamides : Direct Access to Both Pure Geometrical Isomers
- 2019
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In: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 84:21, s. 13540-13548
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Journal article (peer-reviewed)abstract
- A stereodivergent strategy has been developed to access either (E)- or (Z)-isomers of trisubstituted enamides. Starting from an extensive range of ketones, it was possible to synthesize and isolate the desired pure isomer by switching the reaction conditions. Lewis acid activation enables the formation of the (E)-isomers in high stereoselectivity (>90:10) and good yields. On the other hand, the use of a Bronsted acid allows the preparation of the (Z)-isomers, again in high selectivity (up to 99:1), with moderate yields.
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| 5. |
- Naicker, Tricia, et al.
(author)
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Novel tetrahydroisoquinoline based organocatalysts for asymmetric Diels–Alder reactions : insight into the catalytic mode using ROESY NMR and DFT studies
- 2010
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In: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 21:23, s. 2859-2867
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Journal article (peer-reviewed)abstract
- For the first time an organocatalyst bearing a secondary nitrogen within a cyclohexane ring has been evaluated in the asymmetric Diels–Alder reaction. This organocatalyst is also the first of its kind based on a (1R,3S)-6,7-dimethoxy-1-phenyl-1,2,3,4-tetrahydroisoquinoline backbone. These catalysts were tested over a range of dienes and dienophiles and displayed promising chemical conversions of up to 100% with up to 64% ee with triflic acid as the cocatalyst. Density functional theory computational studies and 2D NMR spectroscopy were used to determine the structure of the intermediate iminium ion formed between the most efficient catalyst and cinnamaldehyde. The reaction profile for each of the four possibilities in this reaction were calculated and it was found that the iminium intermediate leading to the major product is higher in energy but kinetically preferred. The activation energies of all possible reaction paths were calculated and the results correlated with the observed products. These experiments revealed that the presence of both (E)- and (Z)-isomers of the cinnamaldehyde were contributing factors for the low enantioselectivity of the reaction products.
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| 6. |
- Olsen, Esben P. K., et al.
(author)
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Experimental and Theoretical Mechanistic Investigation of the Iridium-Catalyzed Dehydrogenative Decarbonylation of Primary Alcohols
- 2015
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 137:2, s. 834-842
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Journal article (peer-reviewed)abstract
- The mechanism for the iridium-BINAP catalyzed dehydrogenative decarbonylation of primary alcohols with the liberation of molecular hydrogen and carbon monoxide was studied experimentally and computationally. The reaction takes place by tandem catalysis through two catalytic cycles involving dehydrogenation of the alcohol and decarbonylation of the resulting aldehyde. The square planar complex IrCl(CO)(rac-BINAP) was isolated from the reaction between [Ir(cod)Cl](2), rac-BINAP, and benzyl alcohol. The complex was catalytically active and applied in the study of the individual steps in the catalytic cycles. One carbon monoxide ligand was shown to remain coordinated to iridium throughout the reaction, and release of carbon monoxide was suggested to occur from a dicarbonyl complex. IrH2Cl(CO)(rac-BINAP) was also synthesized and detected in the dehydrogenation of benzyl alcohol. In the same experiment, IrHCl2(CO)(rac-BINAP) was detected from the release of HCl in the dehydrogenation and subsequent reaction with IrCl(CO)(rac-BINAP). This indicated a substitution of chloride with the alcohol to form a square planar iridium alkoxo complex that could undergo a beta-hydride elimination. A KIE of 1.0 was determined for the decarbonylation and 1.42 for the overall reaction. Electron rich benzyl alcohols were converted faster than electron poor alcohols, but no electronic effect was found when comparing aldehydes of different electronic character. The lack of electronic and kinetic isotope effects implies a rate-determining phosphine dissociation for the decarbonylation of aldehydes.
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| 7. |
- Peters, Bram B. C., et al.
(author)
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Iridium-catalyzed enantioconvergent hydrogenation of trisubstituted olefins
- 2022
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Journal article (peer-reviewed)abstract
- Asymmetric hydrogenation of olefins constitutes a practical and efficient method to introduce chirality into prochiral substrates. However, the absolute majority of the developed methodologies is enantiodivergent and thus require isomerically pure olefins which is a considerable drawback since most olefination strategies produce (E/Z)-mixtures. Although some advances have been reported, a general enantioconvergent hydrogenation featuring a broad functional group tolerance remains elusive. Here, we report the development of a general iridium-catalyzed enantioconvergent hydrogenation of a broad range of functionalized trisubstituted olefins. The substitution pattern around the olefin is critical; whereas α-prochiral olefins can undergo an enantioconvergent hydrogenation, β-prochiral olefins react in an enantiodivergent manner. The presented methodology hydrogenates α-prochiral substrates with excellent control of enantioselection and high isolated yields. Most importantly, both isomerically pure alkenes as well as isomeric mixtures can be hydrogenated to yield the same major enantiomer in excellent enantiomeric excesses which is unusual in transition-metal catalyzed asymmetric hydrogenations.
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| 8. |
- Peters, Byron K., et al.
(author)
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An Enantioselective Approach to the Preparation of Chiral Sulfones by Ir-Catalyzed Asymmetric Hydrogenation
- 2014
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136:47, s. 16557-16562
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Journal article (peer-reviewed)abstract
- Several chiral sulfonyl compounds were prepared using the iridium catalyzed asymmetric hydrogenation reaction. Vinylic, allylic and homoallylic sulfone substitutions were investigated, and high enantioselectivity is maintained regardless of the location of the olefin with respect to the sulfone. Impressive stereoselectivity was obtained for dialkyl substitutions, which typically are challenging substrates in the hydrogenation. As expected, the more bulky Z-substrates were hydrogenated slower than the corresponding E isomers, and in slightly lower enantioselectivity.
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| 9. |
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| 10. |
- Wu, Haibo, et al.
(author)
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Kinetic resolution of racemic allylic alcohols via iridium-catalyzed asymmetric hydrogenation : scope, synthetic applications and insight into the origin of selectivity
- 2021
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In: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 12:5, s. 1937-1943
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Journal article (peer-reviewed)abstract
- Asymmetric hydrogenation is one of the most commonly used tools in organic synthesis, whereas, kinetic resolution via asymmetric hydrogenation is less developed. Herein, we describe the first iridium catalyzed kinetic resolution of a wide range of trisubstituted secondary and tertiary allylic alcohols. Large selectivity factors were observed in most cases (s up to 211), providing the unreacted starting materials in good yield with high levels of enantiopurity (ee up to >99%). The utility of this method is highlighted in the enantioselective formal synthesis of some bioactive natural products including pumiliotoxin A, inthomycin A and B. DFT studies and a selectivity model concerning the origin of selectivity are presented.
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