| 1. |
- He, Lei, et al.
(författare)
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Asymmetric Hydrogenation of Imines Using NHC-Phosphine Iridium Complexes
- 2023
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Ingår i: Asian Journal of Organic Chemistry. - 2193-5807 .- 2193-5815. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- α-Chiral amines represent a frequently observed functional group in pharmaceuticals. Here, the synthesis of such motifs (up to 91% ee) is described by asymmetric hydrogenation of imines catalyzed by NHC,P-iridium complexes. The hydrogenation proceeded smoothly, even under balloon pressure of hydrogen atmosphere. Mechanistic experiments indicated that the reduction most likely advances by a combination of direct hydrogenation and a hydrogen transfer process using either H2 or iPrOH as the reductant, respectively.
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| 2. |
- Li, Xingzhen, et al.
(författare)
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Mono-N-Alkylation of Sulfonamides with Alcohols Catalyzed by Iridium N-Heterocyclic Carbene-Phosphine Complexes
- 2022
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Ingår i: Asian Journal of Organic Chemistry. - : Wiley. - 2193-5807 .- 2193-5815. ; 11:7
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Tidskriftsartikel (refereegranskat)abstract
- A N-heterocyclic carbene-phosphine iridium complex is presented for the efficient and selective mono-N-alkylation of sulfonamides with alcohols based on a borrowing hydrogenation strategy. Herein, water is the only by-product and this methodology thus offers a more environmentally benign and interesting alternative to the use of traditional alkylating reagents. This facile protocol tolerates a large number of (hetero) aromatic and aliphatic sulfonamides as well as (hetero) aromatic and aliphatic alcohols to obtain the desired product is high isolated yield (up to 98%). The alkylation completely retards after the formation of the secondary sulfonamide and no over-alkylation was observed in all cases. The option to run the reaction under solvent-free conditions as well as the scalability of this borrowing hydrogenation are key features of this protocol.
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| 3. |
- Liu, Linpeng, et al.
(författare)
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Ni and Fe catalyzed cascade radical reactions of oxime esters with diselenides
- 2022
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Ingår i: Organic Chemistry Frontiers. - : Royal Society of Chemistry (RSC). - 2052-4129. ; 9:13, s. 3480-3485
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Tidskriftsartikel (refereegranskat)abstract
- A radical cyclization and ring-opening of oxime esters with diselenides was developed. Both Ni(0) and Fe(II) catalysts could be employed for the selenylation of olefin-containing and cyclic oxime ester derivatives. With this method, a variety of functionalized pyrrolines and alkyl nitriles were synthesized in good yields. Moreover, a mechanism involving iminyl radical and carbon-centered radical intermediates was proposed.
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| 4. |
- Peters, Byron K., et al.
(författare)
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An Enantioselective Approach to the Preparation of Chiral Sulfones by Ir-Catalyzed Asymmetric Hydrogenation
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136:47, s. 16557-16562
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Tan, Min, et al.
(författare)
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Recent advances in the metal-catalyzed asymmetric alkene hydrogenation of cyclic conjugated carbonyl compounds
- 2024
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Ingår i: Organic Chemistry Frontiers. - 2052-4129.
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Forskningsöversikt (refereegranskat)abstract
- The transition metal-catalyzed asymmetric hydrogenation of carbon–carbon double bonds is recognized as one of the most straightforward methods for the preparation of stereopure compounds. Chiral cyclic motifs have widespread applications in organic synthesis and can also be prepared via this strategy. This review summarizes the recent advances (2016–2023) in the stereoselective metal-catalyzed hydrogenation of cyclic α,β-unsaturated ketones, lactams and lactones since considerable developments in this regard were made. The applications of these methodologies in synthesis are also outlined where relevant.
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| 6. |
- Verendel, J. Johan, et al.
(författare)
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Chiral Hetero- and Carbocyclic Compounds from the Asymmetric Hydrogenation of Cyclic Alkenes
- 2012
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 18:21, s. 6507-6513
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Tidskriftsartikel (refereegranskat)abstract
- Several types of chiral hetero- and carbocyclic compounds have been synthesized by using the asymmetric hydrogenation of cyclic alkenes. N,P-Ligated iridium catalysts reduced six-membered cyclic alkenes with various substituents and heterofunctionality in good to excellent enantioselectivity, whereas the reduction of five-membered cyclic alkenes was generally less selective, giving modest enantiomeric excesses. The stereoselectivity of the hydrogenation depended more strongly on the substrate structure for the five- rather than the six-membered cyclic alkenes. The major enantiomer formed in the reduction of six-membered alkenes could be predicted from a selectivity model and isomeric alkenes had complementary enantioselectivity, giving opposite optical isomers upon hydrogenation. The utility of the reaction was demonstrated by using it as a key step in the preparation of chiral 1,3-cis-cyclohexane carboxylates.
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| 7. |
- Verendel, J Johan, et al.
(författare)
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Highly Flexible Synthesis of Chiral Azacycles via Iridium-Catalyzed Hydrogenation
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 132:26, s. 8880-8881
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Tidskriftsartikel (refereegranskat)abstract
- A range of saturated chiral azacycles has been prepared in high yield and with high selectivity from simple starting materials. A modular approach with ring-closing metathesis as a key step was used to produce a number of five-, six-, and seven-membered cyclic alkenes. Asymmetric hydrogenation catalyzed by N,P-ligated iridium complexes gave saturated azacycles in high optical purity. This methodology was demonstrated in the synthesis of a pharmaceutical precursor.
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| 8. |
- Yang, Jianping, et al.
(författare)
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Catalytic enantioselective synthesis of fluoromethylated stereocenters by asymmetric hydrogenation
- 2022
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 13:29, s. 8590-8596
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Tidskriftsartikel (refereegranskat)abstract
- Fluoromethyl groups possess specific steric and electronic properties and serve as a bioisostere of alcohol, thiol, nitro, and other functional groups, which are important in an assortment of molecular recognition processes. Herein we report a catalytic method for the asymmetric synthesis of a variety of enantioenriched products bearing fluoromethylated stereocenters with excellent yields and enantioselectivities. Various N,P-ligands were designed and applied in the hydrogenation of fluoromethylated olefins and vinyl fluorides.
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| 9. |
- Zhou, Taigang, 1982-
(författare)
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Asymmetric Hydrogenation of Functionalized Olefins Using N,P-Ligated Iridium Complexes
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transition-metal-catalyzed asymmetric hydrogenation is one of the most efficient, straightforward, and well-established methods for preparing enantiomerically enriched compounds. Over the past decades, significant progress has been made with iridium, rhodium and ruthenium complexes to asymmetric hydrogenate a selection of olefins, such as, α,β-unsaturated carboxylic acid derivatives, ketones, imines and phosphonates. Although these metals have been applied successfully in the hydrogenation of olefins, they differ in their substrate tolerance. Ruthenium and rhodium based catalysts require a coordinating group in the vicinity of the C=C bond. However, iridium based catalysts do not require this coordinating group, hence, asymmetric hydrogenation with iridium catalysts has been widely used for both functionalized and unfunctionalized olefin substrates. This thesis focuses on expanding the substrate scope for asymmetric hydrogenation using chiral N,P-ligated iridium catalysts. Papers I and II investigate the asymmetric hydrogenation of prochiral N-heterocyclic compounds prepared by ring-closing metathesis using the iridium catalysts developed in our group. These substrates are interesting as they bear resemblance to pharmaceutically active compounds and therefore have tremendous value in medicinal chemistry. Excellent enantioselectivities, up to >99% ee and conversions were obtained. In papers III and IV we synthesized many unsaturated acyclic and cyclic sulfones with varying substitution patterns. The sulfones were subjected to hydrogenation using our N,P-ligated iridium catalysts, producing the chiral sulfone products in high enantiomeric excess (up to 99% ee). This methodology was combined with the Ramberg-Bäcklund reaction, offering a novel route to chiral allylic and homoallylic compounds. In addition to obtaining these chiral compounds in good yields, no decrease in enantiomeric excess was observed after the Ramberg-Bäcklund reaction. This strategy has been applied in the preparation of the chiral building block for renin inhibitors.
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| 10. |
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