| 1. |
- Chakka, Sai Kumar, et al.
(författare)
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Asymmetric conjugate addition of thioglycolate to a range of chalcones using tetrahydroisoquinoline (TIQ) N,N '-dioxide ligands
- 2012
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Ingår i: Tetrahedron. - : Elsevier BV. - 0957-4166 .- 1362-511X. ; 23:8, s. 616-622
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel TIQ based N,N'-oxide ligands were synthesised and screened for their catalytic activity in the enantioselective conjugate addition of thioglycolate to chalcones. Bulky groups on the side chain of the TIQ backbone provided the highest enantioselectivity of up to 88% with 10 mol % catalyst loading. It was also observed that these reactions proceeded optimally in the presence of dichloromethane as a solvent. Screening of various metals emphasized La(OTf)(3) as the ideal pre-catalyst for this particular reaction.
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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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