Asymmetric creation of quaternary carbon centers

Fuji, Kaoru

doi:10.1021/cr00022a005

Cited by 713 publications

(119 citation statements)

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“…9,10 This idea is highlighted by examples in ringclosing metathesis of trienes, 11 esterification of symmetric diols, 12 conjugate addition, 13,14 Ullmann coupling, 15 Suzuki coupling, 16 allylic substitution, 17 silylation of diols, 18 and oxidation. 19 Notably, C−C or C−N bonds are not formed or broken at the stereogenic center obtained through desymmetrization.…”

Section: ■ Introductionmentioning

confidence: 99%

Zirconium-Catalyzed Desymmetrization of Aminodialkenes and Aminodialkynes through Enantioselective Hydroamination

2015

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The catalytic addition of alkenes and amines (hydroamination) typically provides α-or β-amino stereocenters directly through C-N or C-H bond formation. Alternatively, desymmetrization reactions of symmetrical aminodialkenes or aminodialkynes provide access to stereogenic centers with the position controlled by the substrate's structure. In the present study of an enantioselective zirconium-catalyzed hydroamination, stereocenters resulting from C-N bond formation and desymmetrization of a prochiral quaternary center are independently controlled by the catalyst and reaction conditions. Using a single catalyst, the method provides selective access to either diastereomer of optically enriched five-, six-, and seven-membered cyclic amines from aminodialkenes and enantioselective synthesis of five-, six-, and seven-membered cyclic imines from aminodialkynes. Experiments on hydroamination of aminodialkenes testing the effects of the catalyst:substrate ratio, the absolute concentration of the catalyst, and the absolute initial concentration of the primary amine substrate show that the latter parameter strongly influences the stereoselectivity of the desymmetrization process, whereas the absolute configuration of the α-amino stereocenter generated by C-N bond formation is not affected by these parameters. Interestingly, isotopic substitution (H2NR vs D2NR) of the substrate enhances the stereoselectivity of the enantioselective and diastereoselective processes in aminodialkene cyclization and the peripheral stereocenter in aminodialkyne desymmetrization/cyclization. ABSTRACT: The catalytic addition of alkenes and amines (hydroamination) typically provides α-or β-amino stereocenters directly through C−N or C−H bond formation. Alternatively, desymmetrization reactions of symmetrical aminodialkenes or aminodialkynes provide access to stereogenic centers with the position controlled by the substrate's structure. In the present study of an enantioselective zirconium-catalyzed hydroamination, stereocenters resulting from C−N bond formation and desymmetrization of a prochiral quaternary center are independently controlled by the catalyst and reaction conditions. Using a single catalyst, the method provides selective access to either diastereomer of optically enriched five-, six-, and seven-membered cyclic amines from aminodialkenes and enantioselective synthesis of five-, six-, and seven-membered cyclic imines from aminodialkynes. Experiments on hydroamination of aminodialkenes testing the effects of the catalyst:substrate ratio, the absolute concentration of the catalyst, and the absolute initial concentration of the primary amine substrate show that the latter parameter strongly influences the stereoselectivity of the desymmetrization process, whereas the absolute configuration of the α-amino stereocenter generated by C−N bond formation is not affected by these parameters. Interestingly, isotopic substitution (H 2 NR vs D 2 NR) of the substrate enhances the stereoselectivity of the enantioselective and diastereoselecti...

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Section: ■ Introductionmentioning

confidence: 99%

Zirconium-Catalyzed Desymmetrization of Aminodialkenes and Aminodialkynes through Enantioselective Hydroamination

2015

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“…When the four substituents differ, quaternary stereocenters become a singular challenge for achieving efficient asymmetric syntheses of chiral organic molecules (1)(2)(3)(4). The invention of catalytic methods for asymmetric synthesis is one of the foremost recent achievements of chemistry (5), with the 2001 Nobel Prize in Chemistry recognizing William S. Knowles, Ryoji Noyori, and K. Barry Sharpless for their pioneering development of catalytic asymmetric hydrogenation and oxidation reactions.…”

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confidence: 99%

Catalytic Asymmetric Synthesis of all‐Carbon Quaternary Stereocenters

Douglas

Overman

2004

ChemInform

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Only a few catalytic asymmetric COC bond-forming reactions have been shown to be useful for constructing all-carbon quaternary stereocenters. This Perspective examines the current state of such methods. Carbon atoms bonded to four carbon substituents (all-carbon quaternary centers) pose a particular challenge for synthesis because creation of such centers is complicated by steric repulsion between the carbon substituents. When the four substituents differ, quaternary stereocenters become a singular challenge for achieving efficient asymmetric syntheses of chiral organic molecules (1-4). The invention of catalytic methods for asymmetric synthesis is one of the foremost recent achievements of chemistry (5), with the 2001 Nobel Prize in Chemistry recognizing William S. Knowles, Ryoji Noyori, and K. Barry Sharpless for their pioneering development of catalytic asymmetric hydrogenation and oxidation reactions. At present, many broadly useful methods for catalytic asymmetric oxidation and reduction exist; however, far fewer catalytic asymmetric methods for forming COC bonds have been invented to date (5). As disclosures in this special feature will attest, this latter area of catalytic asymmetric synthesis is a current focus of intense investigation worldwide.At present only a few catalytic asymmetric COC bond-forming reactions have been shown to be useful for constructing quaternary carbons, undoubtedly reflecting the additional steric challenge involved in forming all-carbon quaternary centers. This Perspective will examine the current state of such methods. The focus will be on reactions for which some generality has been documented, and several examples exist of reactions that proceed with enantiomeric selectivities of at least 9:1 [enantiomeric excesses (ees) Ͼ80%]. The discussion is organized by general reaction types that have proven useful, not by the more commonly used organizations that focus on one specific transformation or one family of asymmetric catalysts. It is hoped that this organization will highlight the many opportunities that exist for future discoveries in this area. The less general approach for forming allcarbon quaternary stereocenters in which a group-selective catalytic asymmetric reaction is used to desymmetrize a prochiral intermediate containing a quaternary carbon will be briefly mentioned also. No attempt to summarize this latter field will be made, as any catalytic asymmetric reaction could in principle be used in this approach. In four areas, catalytic methods for directly forming all-carbon stereocenters are most developed: Diels-Alder reactions, the combination of chiral carbon nucleophiles with carbon electrophiles, reactions of allylmetal intermediates with carbon nucleophiles, and intramolecular Heck reactions. Our discussion will begin with these reaction types. Asymmetric Diels-Alder ReactionsThe Diels-Alder reaction provides two approaches for forming quaternary stereocenters contained within the cyclohexene framework (Scheme 1). In reactions of type I, electron-rich dienes c...

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“…The interest in synthesizing biologically active products containing stereogenic carbon atoms has notably increased over the last decade, and chirality is currently of major importance in drug discovery and development 9 . With the development of new technologies, the preparation of enantiomerically pure compounds is frequently requested because of the different activities of drug enantiomers in pharmaceutical applications [10][11][12] .…”

Section: Introductionmentioning

confidence: 99%