| 1. |
- Cele, Zamani E. D., et al.
(författare)
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Catalytic asymmetric carbon-carbon bond forming reactions catalyzed by tetrahydroisoquinoline (TIQ) N,N '-dioxide ligands
- 2013
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Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 24:4, s. 191-195
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Tidskriftsartikel (refereegranskat)abstract
- The use of TIQ-N,N'-dioxide ligands in asymmetric C-C bond forming reactions is described. In the Michael addition of cyclohexane-1,3-dione and malonates to beta,gamma-unsaturated alpha-ketoesters, excellent yields (up to 93%) and moderate to good enantioselectivities (70-89% ee) were obtained. The catalytic hetero-ene reaction of 2-methoxypropene with phenylglyoxal gave the ene product in excellent yield (95%) with moderate enantioselectivity (77% ee). The catalyst system performed well at temperatures ranging from 0 to 30 degrees C and relatively low catalyst loading (0.2-5 mol %) with dichloromethane being the preferred solvent for all reactions.
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| 2. |
- Chakka, Sai Kumar, et al.
(författare)
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Iridium-catalyzed asymmetric hydrogenation of olefins using TIQ phosphine-oxazoline ligands
- 2010
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Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 21:18, s. 2295-2301
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Tidskriftsartikel (refereegranskat)abstract
- A novel family of tetrahydroisoquinoline (TIQ) phosphine-oxazoline ligands and four corresponding iridium complexes have been developed and applied to the asymmetric hydrogenation of unfunctionalized olefins. The results showed that the best conversion rates were observed in up to 99% with an enantiomeric excess of 91%.
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| 3. |
- Chakka, Sai Kumar, et al.
(författare)
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Synthesis and Screening of C-1-Substituted Tetrahydroisoquinoline Derivatives for Asymmetric Transfer Hydrogenation Reactions
- 2010
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; :5, s. 972-980
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Tidskriftsartikel (refereegranskat)abstract
- Tetrahydroisoquinoline (TIQ) derivatives exhibit good biological activity. However, utilization of TIQ compounds in asymmetric catalysis is limited. This paper presents a series of TIQ derivatives in asymmetric transfer hydrogenation (ATH) reactions. Chiral TIQ amino alcohol ligands were synthesized and screened for the ATH reaction of aromatic ketones. The effect of a cis- and trans-phenyl substitution at the C-1 position on the ligand backbone was investigated both experimentally and computationally. The results showed that the trans orientation on the TIQ scaffold yields higher turnover rates with a selectivity of 94% ee obtained at room temperature with an Ru complex. The cis isomer results in a high turnover rate with no selectivity. The trans isomer gave 99% ee at lower temperatures. Furthermore, it was observed that substitution at the C-3-alpha position results in a drop of the enantioselectivity and the reactivity of the catalyst.
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| 4. |
- Kawthekar, Rahul B., et al.
(författare)
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Synthesis of tetrahydroisoquinoline (TIQ)-oxazoline ligands and their application in enantioselective Henry reactions
- 2010
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Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 21:7, s. 846-852
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Tidskriftsartikel (refereegranskat)abstract
- A novel family of eleven new tetrahydroisoquinoline (TIQ)-oxazoline intermediates and five corresponding copper(II) catalysts has been developed and applied to the catalytic asymmetric Henry reaction of various aldehydes with nitromethane to provide beta-hydroxy nitroalkanes in high conversion (>99%) This paper describes the synthesis of the TIQ compounds from L-dihydroxyphenylalanine (L-DOPA) as the starting material The chiral ligands were complexed in situ with various transition metals such as Cu, Sc, Co, Zn, Ni and Mn and tested as a chiral catalyst for the Henry reaction The reaction was optimized in terms of the metal, counter ion, solvent, temperature and over a range of substrates The corresponding catalyst with copper(II) acetate and 2-propanol as the solvent provides the best enantioselectivities (up to 77% ee) of the corresponding nitroalcohol for 4-chlorobenzaldehyde.
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| 5. |
- Pawar, Sunayna S., et al.
(författare)
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Comparison of Tetrahydroisoquinoline (TIQ) Thiazole and Oxazoline Ligands for Asymmetric Henry Reactions
- 2012
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Ingår i: South African Journal of Chemistry. - 0379-4350 .- 1996-840X. ; 65, s. 23-29
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel C-1 symmetric thiazole ligands with a tetrahydroisoquinoline (TIQ) backbone were synthesized. Their application in the catalytic asymmetric Henry reaction was investigated with comparison to a corresponding TIQ oxazoline ligand. The Cu(II)-oxazoline complex was more reactive and furnished moderate enantioselectivities up to 61:36 (syn:anti) with 75:25 diastereomeric excess, while the Cu(II)-thiazole complexes had lower selectivity. This is the first example where a direct comparison between an N, N-type thiazole and oxazoline ligands has been studied.
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| 6. |
- Peters, Byron K., et al.
(författare)
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Synthesis of tetrahydroisoquinoline-diamine ligands and their application in asymmetric transfer hydrogenation
- 2010
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Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 21:6, s. 679-687
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Tidskriftsartikel (refereegranskat)abstract
- The use of the tetrahydroisoquinoline scaffold is well documented in biologically active compounds. However, reports of the utilisation of tetrahydroisoquinoline compounds in asymmetric catalysis are limited. The synthesis of novel diamine ligands possessing the tetrahydroisoquinoline (tetrahydroisoquinoline) backbone and evaluation of their activity in the asymmetric transfer hydrogenation of acetophenone are presented. The diamine ligands in conjunction with i-PrOH as the hydrogen source and [RhCl2(Cp*)](2) as the metal precursor proved to be the most effective of the tetrahydroisoquinoline derivatives for this catalytic system. Water was found to have a profound influence on the enantioselectivity of the reaction. Optimisation of the amount water, i-PrOH and catalytic loading content rendered the best result of 70% enantioselectivity for the (S)-1-phenylethanol isomer product.
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| 7. |
- Wu, Haibo, et al.
(författare)
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Site- and Enantioselective Iridium-Catalyzed Desymmetric Mono-Hydrogenation of 1,4-Dienes
- 2021
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 60:35, s. 19428-19434
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Tidskriftsartikel (refereegranskat)abstract
- The control of site selectivity in asymmetric mono-hydrogenation of dienes or polyenes remains largely underdeveloped. Herein, we present a highly efficient desymmetrization of 1,4-dienes via iridium-catalyzed site- and enantioselective hydrogenation. This methodology demonstrates the first iridium-catalyzed hydrogenative desymmetriation of meso dienes and provides a concise approach to the installation of two vicinal stereogenic centers adjacent to an alkene. High isolated yields (up to 96%) and excellent diastereo- and enantioselectivities (up to 99:1 d.r. and 99% ee) were obtained for a series of divinyl carbinol and divinyl carbinamide substrates. DFT calculations reveal that an interaction between the hydroxy oxygen and the reacting hydride is responsible for the stereoselectivity of the desymmetrization of the divinyl carbinol. Based on the calculated energy profiles, a model that simulates product distribution over time was applied to show an intuitive kinetics of this process. The usefulness of the methodology was demonstrated by the synthesis of the key intermediates of natural products zaragozic acid A and (+)-invictolide.
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| 8. |
- Yang, Jianping, et al.
(författare)
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Combined Theoretical and Experimental Studies Unravel Multiple Pathways to Convergent Asymmetric Hydrogenation of Enamides
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:51, s. 21594-21603
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Tidskriftsartikel (refereegranskat)abstract
- We present a highly efficient convergent asymmetric hydrogenation of E/Z mixtures of enamides catalyzed by N,P–iridium complexes supported by mechanistic studies. It was found that reduction of the olefinic isomers (E and Z geometries) produces chiral amides with the same absolute configuration (enantioconvergent hydrogenation). This allowed the hydrogenation of a wide range of E/Z mixtures of trisubstituted enamides with excellent enantioselectivity (up to 99% ee). A detailed mechanistic study using deuterium labeling and kinetic experiments revealed two different pathways for the observed enantioconvergence. For α-aryl enamides, fast isomerization of the double bond takes place, and the overall process results in kinetic resolution of the two isomers. For α-alkyl enamides, no double bond isomerization is detected, and competition experiments suggested that substrate chelation is responsible for the enantioconvergent stereochemical outcome. DFT calculations were performed to predict the correct absolute configuration of the products and strengthen the proposed mechanism of the iridium-catalyzed isomerization pathway.
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| 9. |
- Zheng, Jia, et al.
(författare)
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Iridium-catalysed enantioselective formal deoxygenation of racemic alcohols via asymmetric hydrogenation
- 2019
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Ingår i: NATURE CATALYSIS. - : NATURE PUBLISHING GROUP. - 2520-1158. ; 2:12, s. 1093-1100
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Tidskriftsartikel (refereegranskat)abstract
- Asymmetric hydrogenation of alkenes is one of the most powerful tools for the preparation of optically active compounds. However, to achieve high enantioselectivity, the starting olefin in most cases needs to be isomerically pure in either the cis or the trans form. Generally, most olefination protocols provide olefins as isomeric mixtures that are difficult to separate, and in many cases also generate lots of waste. In contrast, the synthesis of racemic alcohols is straightforward and highly atom-efficient, with products that are easier to purify. Here, we describe a strategy that enables rapid access to chiral alkanes via enantioconvergent formal deoxygenation of racemic alcohols. Mechanistic studies indicate an Ir-mediated elimination of water and subsequent in situ hydrogenation. This approach allows rapid and efficient assembly of chiral intermediates and is exemplified in the total synthesis of antidepressant sertraline and sigma(2) receptor PB 28.
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| 10. |
- Zheng, Jia, et al.
(författare)
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The Effect of Conformational Freedom vs Restriction on the Rate in Asymmetric Hydrogenation : Iridium-Catalyzed Regio- and Enantioselective Monohydrogenation of Dienones
- 2024
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Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 30:13
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal-catalyzed asymmetric hydrogenation constitutes an efficient strategy for the preparation of chiral molecules. When dienes are subjected to hydrogenation, control over regioselectivity still presents a large challenge and the fully saturated alkane is often yielded. A few successful monohydrogenations of dienes have been reported, but hitherto these are only efficient for dienes comprised of two distinctly different olefins. Herein, the reactivity of a conjugated carbonyl compound as a function of their conformational freedom is studied, based on a combined experimental and theoretical approach. It was found that alkenes in the (s)-cis conformation experience a large rate acceleration while (s)-trans restrained alkenes undergo hydrogenation slowly. Ultimately, this reactivity aspect was exploited in a novel method for the monohydrogenation of dienes based on conformational restriction ((s)-cis vs (s)-trans). This mode of discrimination conceptually differs from existing monohydrogenations and dienones constructed of two olefins similar in nature could efficiently be hydrogenated to the chiral alkene (up to 99 % ee). The extent of regioselection is even powerful enough to overcome the conventional reactivity order of substituted olefins (di>tri>tetra). This high yielding and atom-economical protocol provides an interesting opportunity to instal a stereogenic center on a carbocycle, while leaving a synthetically useful alkene untouched.
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