New Chiral <i>N</i>, 5‐Ligands with Thiophenyl at Benzylic Position. Palladium (II)‐catalyzed Enantioselective Allylic Alkylation

Wu, Hao; Wu, Xiao-Ning; Hou, Xue‐Long; Dai, Li‐Xin; Wang, Quanrui

doi:10.1002/cjoc.20020200903

Cited by 12 publications

References 15 publications

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Highly Enantioselective Iridium‐Catalyzed Hydrogenation of Trisubstituted Olefins, α,β‐Unsaturated Ketones and Imines with Chiral Benzylic Substituted P,N Ligands

Chen

Hou

2010

Adv Synth Catal

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The benzylic substituted P,N ligands, diphosphinobenzyloxazolines, showed their high catalytic activity as well as asymmetric induction in the iridium-catalyzed asymmetric hydrogenation of unfunctionalized alkenes, a,b-unsaturated esters, allyl alcohols, a,b-unsaturated ketones, and imines, providing the corresponding chiral products in high ee with high conversion.Keywords: asymmetric hydrogenation; imines; iridium; P,N ligands; unfunctionalized olefins; a,b-unsaturated ketonesThe enantioselective hydrogenation as one of the most powerful tools in asymmetric catalysis for the preparation of optically active compounds has attracted great attention. Different transition metals with chiral ligands have been used as catalysts in the hydrogenation reactions of a variety of unsaturated compounds.[1] Among them, chiral iridium complexes have showed their unique asymmetric induction and catalytic activity for some substrates, [2] especially for non-functionalized alkenes, [2d-g] enamines, [2h,i,x] imines, [2j-m,w] quinolines, [2n-t] a,b-unsaturated ketones, [3] and carboxylic acid derivatives. [2u] In spite of the great progress achieved, only a limited number of ligands have been found to be effective in iridium-catalyzed asymmetric hydrogenation, although a wide variety of ligands with different frameworks has been synthesized and used in asymmetric catalysis.[4] Recently, we developed benzylic substituted ligands and showed their catalytic activity as well as asymmetric induction (Scheme 1).[5] It was deduced that the ligands with one more carbon atom have increased tether length between the donor atoms and this makes the transition metal complexes have more conformers to fit different substrates. Herein we report the Ir-catalyzed asymmetric hydrogenation of non-functionalized alkenes as well as imines and a,b-unsaturated ketones using the catalyst derived from benzylic substituted ligand 3, providing the corresponding products in high enantioselectivities.Asymmetric hydrogenation of unfunctionalized olefins had been a challenge for a long time and the breakthrough appeared when Pfaltz used Ir catalysts with the famous PHOX ligands.[3a] Since then, many P,N ligands were used in the Ir-catalyzed asymmetric hydrogenation of this type of olefins, some of which provided products in high enantioselectivity. Thus, the asymmetric hydrogenation of olefin 4a was chosen to test the effectiveness of the ligand. It showed that product 6a in 97% ee with 100% conversion was obtained when 0.3 mol% of catalyst 5a under 50 bar of hydrogen pressure at 25 8C was used. Encouraged by this result, the impact of different aryl groups on P as well as the substituents on the oxazoline ring on the reaction was investigated [Eq. (1), Table 1]. It can be Scheme 1. Structure of benzylic substituted ligands.

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Highly Enantioselective Iridium‐Catalyzed Hydrogenation of Trisubstituted Olefins, α,β‐Unsaturated Ketones and Imines with Chiral Benzylic Substituted P,N Ligands

Chen

Hou

2010

Adv Synth Catal

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Metallkatalysierte enantioselektive Allylierungen in der asymmetrischen Synthese

Lu¹,

Ma²

2007

Angewandte Chemie

431

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Durch metallkatalysierte enantioselektive Allylierungen, die unter Substitution von Allylmetall‐Zwischenstufen mit zahlreichen Nucleophilen oder als allylische SN2′‐Substitution verlaufen, werden in Gegenwart ausgewählter Kombinationen aus Metallen und chiralen Liganden C‐H‐, C‐C‐, C‐O‐, C‐N‐, C‐S‐ und andere Bindungen mit sehr hoher asymmetrischer Induktion geknüpft. Die Reaktionen sind mit einer Vielzahl funktioneller Gruppen vereinbar und wurden erfolgreich in der Synthese vieler Naturstoffe und neuer chiraler Verbindungen verwendet.

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Metal‐Catalyzed Enantioselective Allylation in Asymmetric Synthesis

2007

Angew Chem Int Ed

1,358

431

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Metal-catalyzed enantioselective allylation, which involves the substitution of allylic metal intermediates with a diverse range of different nucleophiles or S(N)2'-type allylic substitution, leads to the formation of C-H, -C, -O, -N, -S, and other bonds with very high levels of asymmetric induction. The reaction may tolerate a broad range of functional groups and has been applied successfully to the synthesis of many natural products and new chiral compounds.

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New Chiral N, 5‐Ligands with Thiophenyl at Benzylic Position. Palladium (II)‐catalyzed Enantioselective Allylic Alkylation

Cited by 12 publications

References 15 publications

Highly Enantioselective Iridium‐Catalyzed Hydrogenation of Trisubstituted Olefins, α,β‐Unsaturated Ketones and Imines with Chiral Benzylic Substituted P,N Ligands

Highly Enantioselective Iridium‐Catalyzed Hydrogenation of Trisubstituted Olefins, α,β‐Unsaturated Ketones and Imines with Chiral Benzylic Substituted P,N Ligands

Metallkatalysierte enantioselektive Allylierungen in der asymmetrischen Synthese

Metal‐Catalyzed Enantioselective Allylation in Asymmetric Synthesis

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