| 1. |
- Dayaker, G., et al.
(författare)
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Enantioselective deprotometalation of alkyl ferrocenecarboxylates using bimetallic bases
- 2021
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Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1144-0546 .- 1369-9261. ; 45:48, s. 22579-22590
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Tidskriftsartikel (refereegranskat)abstract
- The enantioselective deprotometalation of alkyl ferrocenecarboxylates (FcCO(2)R) using mixed lithium-zinc or lithium-cadmium bases is described. By using FcCO(2)Me as the substrate, chiral lithium alkyl-amidozincates prepared from exo-(alpha R)- or endo-(alpha S)-N-(alpha-phenylethyl)bornylamine (H-exo-born-R or H-endo-born-S) were tested; the best results (27% yield and 62% ee in favor of the R-P enantiomer) were obtained by using Bu-2(endo-born-S)ZnLi in tetrahydrofuran (THF) at -30 degrees C before iodolysis. Due to the low compatibility of FcCO(2)Me with alkyl-containing lithium zincates, 1 : 1 mixtures of lithium and zinc amides were tested. Chiral (H-exo-born-R or H-endo-born-S) or/and achiral (lithium 2,2,6,6-tetramethylpiperidide or lithium diisopropylamide) secondary amines gave good results, the best (81% yield and 44% ee in favor of the R-P enantiomer) being obtained by using (endo-born-S)(3)ZnLi in THF at room temperature. Among other secondary amines also prepared and/or tested, commercial (S,S)-bis(alpha-phenylethyl)amine (H-PEA-S) proved promising. After optimization of the reaction conditions, the best enantioselectivity (26% yield and 80% ee in favor of the RP enantiomer) was observed by treating a THF solution of FcCO(2)Me and Zn(PEA-S)(2) with Li-PEA-S at -80 degrees C before iodolysis. That no reaction took place with cadmium instead of zinc suggests the formation of 'ate complexes upon treatment of Cd(PEA-S)(2) by Li-PEA-S while Zn(PEA-S)(2) and Li-PEA-S would rather work in tandem (Li-PEA-S as the base and Zn(PEA-S)(2) as the in situ trap for the formed ferrocenyllithium). While FcCO(2)Me, FcCO(2)tBu and FcCO(2)iPr could be converted into their racemic 2-iodinated derivatives with a yield of 84 to 87% by employing LiTMP (2 equiv.) in the presence of ZnCl2.TMEDA (1 equiv.) as an in situ trap, their enantioselective deprotometalation rather required Li-PEA-S together with Zn(PEA-S)(2) to produce the enantio-enriched derivatives with yields of 45-82% and 71% ee.
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| 2. |
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| 3. |
- Dayaker, G., et al.
(författare)
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Enantioselective Metalation of N,N-Diisopropylferrocenecarboxamide and Methyl Ferrocenecarboxylate Using Lithium-Metal Chiral Bases
- 2012
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X. ; :30, s. 6051-6057
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Tidskriftsartikel (refereegranskat)abstract
- Enantioselective deprotonative metalations of substituted ferrocenes using mixed lithium-metal bases are described. Using N,N-diisopropylferrocenecarboxamide as substrate, magnesium, iron, cobalt, zinc, and cadmium were tested as metals in bis[(S)-1-phenylethyl]amido-based combinations; after interception of the metalated species with iodine, very high enantiomeric excess (96?%) but low yield was obtained with cobalt, whereas zinc and cadmium only gave 27 and 30?%?ee, respectively, but in excellent yields. The small alkyl groups methyl and ethyl were identified as particularly suitable in the reaction using the putative dialkyl bis[(S)-1-phenylethyl]amido-based lithium and dilithium zincates. The dimethyl dilithium zincate was selected for a study of dependency on the temperature, reaction time, and amount of base. Increased enantioselectivities with temperature, reaction time, and amount of base were noted (ee = 86?% at 0 degrees C after 2 h, 2 equiv. of base). The best result using methyl ferrocenecarboxylate as substrate was observed without alkyl ligand.
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| 4. |
- Gayet, Arnaud, 1977-
(författare)
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Development of New Chiral Bicyclic Ligands : Applications in Catalytic Asymmetric Transfer Hydrogenation, Epoxidations, and Epoxide Rearrangements
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the synthesis and application of new chiral bicyclic ligands and their application in asymmetric catalysis. The studies involved: [i] The development of novel chiral bicyclic amino sulfur ligands and their use in transfer hydrogenation. [ii] The development of the kinetic resolution of racemic epoxide through the use of chiral lithium amides. [iii] The synthesis and application of chiral bicyclic amine in the organocatalysed epoxidation of alkenes. [iv] Development and application of new chiral diamine ligands in the rearrangement of epoxides into allylic alcohols.[i] The preparation of two-series of amino thiol ligands based on the structure of camphor is described, together with their application in the iridium-catalysed asymmetric transfer hydrogenation of acetophenone using isopropanol as the hydrogen source. Excellent activity and good enantioselectivity have been achieved using 2 mol% of chiral ligand in combination with [IrCl(COD)]2.[ii] The chiral diamines (1S,3R,4R)-3-(pyrrolidine-1-ylmethyl)-2-aza-bicyclo[2.2.1]heptane and its (2R,5R)-dimethylpyrrolidine derivative were applied to the kinetic resolution of a variety of racemic 5-7 membered cycloalkene oxides with lithium diisopropylamide (LDA) as the bulk base. Using 5 mol% of the chiral diamines, both unreacted epoxides and allylic alcohols could be produced in enantiomeric excess up to 99%.[iii] The synthesis of chiral bicyclic amines and their use in the organocatalysed epoxidation of alkene has been described. Using a substoichiometric amount of the chiral amines and aldehydes as ligands precursors, with Oxone® as oxidant, a good activity but moderate enantioselectivity was observed for the epoxidation of trans-stilbene. [iv] The preparation of 6-substituted-7-bromo-aza-bicyclo[2.2.1]heptanes via nucleophilic addition of organocopper reagents to 3-bromo-1-azoniatricyclo[2.2.1.0]heptyle bromide has been described. These compounds have been utilised as chiral building blocks in the preparation of novel chiral diamine ligands, which have been successfully applied to the catalysed asymmetric rearrangement of epoxide into the corresponding allylic alcohol.
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| 6. |
- Tolstoy, Päivi, 1979-
(författare)
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Synthesis and Evaluation of N,P-Chelating Ligands in Asymmetric Transition-Metal-Catalyzed Reactions : Ir-Catalyzed Asymmetric Hydrogenation and Pd-Catalyzed Asymmetric Intermolecular Heck Reaction
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes synthesis of new chiral N,P ligands and their evaluation in two types of asymmetric transition-metal catalyzed reactions. The first part of the thesis describes studies in iridium-catalyzed asymmetric hydrogenation. A new class of chiral N,P ligands, imidazole-phosphines, was synthesized and evaluated in the Ir-catalyzed asymmetric hydrogenation of olefins (Paper I). The new ligands proved to be highly efficient and enantioselective in the reaction. Because the substrate scope of Ir-catalyzed asymmetric hydrogenation is still limited to certain types of test substrates, new substrate classes with importance in medicinal and materials chemistry were investigated. Vinyl fluorides were efficiently hydrogenated to fluorine-containing chiral centers by the iridium catalysts with imidazole-phosphine ligands (Paper I). To obtain CF3-bearing chiral centers, we hydrogenated CF3-substituted olefins (Paper II). Ir-catalyzed asymmetric hydrogenation was highly enantioselective for the functionalized CF3-substituted olefins and the resulting chiral products can be valuable in design of materials such as LCD screens. Ir-catalyzed asymmetric hydrogenation was also evaluated as a route to diarylmethine chiral centers (Paper III). A wide range of new chiral compounds possessing a diarylmethine chiral center was obtained. The second part of the thesis deals with asymmetric intermolecular Heck reaction utilizing N,P ligands. The N,P ligand class of thiazole-phosphines was evaluated in the Heck reaction (Paper IV) and gave high enantioselectivity. Further, the intermolecular Heck reaction was examined using computational and experimental studies (Paper V). This study led to a better understanding of the enantioselectivity in the reaction.
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