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Engaging Chiral Cationic Intermediat...

Zhang, Hu.

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Engaging Chiral Cationic Intermediates by Anion-Binding in Asymmetric Catalysis.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Engaging Chiral Cationic Intermediates by Anion-Binding in Asymmetric Catalysis./
作者:	Zhang, Hu.
面頁冊數:	146 p.
附註:	Source: Dissertation Abstracts International, Volume: 77-09(E), Section: B.
Contained By:	Dissertation Abstracts International77-09B(E).
標題:	Organic chemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10102908
ISBN:	9781339665368

Engaging Chiral Cationic Intermediates by Anion-Binding in Asymmetric Catalysis.
Zhang, Hu.

Engaging Chiral Cationic Intermediates by Anion-Binding in Asymmetric Catalysis. - 146 p.

Source: Dissertation Abstracts International, Volume: 77-09(E), Section: B.

Thesis (Ph.D.)--Harvard University, 2016.

Anion-binding catalysis by dual hydrogen-bond donors such as ureas and squaramides has been demonstrated as a powerful strategy for the development of highly enantioselective transformations involving prochiral cationic intermediates, such as iminium ions, oxocarbenium ions, carbenium ions, and episulfonium ions. The research described in this dissertation explores the ability of dual H-bond donor catalysts to engage chiral cationic intermediates and to induce enantioselectivity in transformations involving such intermediates.

ISBN: 9781339665368Subjects--Topical Terms:

523952
Organic chemistry.

Engaging Chiral Cationic Intermediates by Anion-Binding in Asymmetric Catalysis.
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245 1 0 $a Engaging Chiral Cationic Intermediates by Anion-Binding in Asymmetric Catalysis.
300 $a 146 p.
500 $a Source: Dissertation Abstracts International, Volume: 77-09(E), Section: B.
500 $a Adviser: Eric N. Jacobsen.
502 $a Thesis (Ph.D.)--Harvard University, 2016.
520 $a Anion-binding catalysis by dual hydrogen-bond donors such as ureas and squaramides has been demonstrated as a powerful strategy for the development of highly enantioselective transformations involving prochiral cationic intermediates, such as iminium ions, oxocarbenium ions, carbenium ions, and episulfonium ions. The research described in this dissertation explores the ability of dual H-bond donor catalysts to engage chiral cationic intermediates and to induce enantioselectivity in transformations involving such intermediates.
520 $a In Chapters 1, we provide an overview of the progress and challenges in the development of enantioselective halo- and seleno-functionalization reactions, which proceed via three-membered ring cationic halonium or seleniranium ions.
520 $a In Chapter 2, we report a highly enantioselective selenocyclization reaction that is promoted by the combination of a chiral squaramide catalyst, a mineral acid, and an achiral Lewis base. Mechanistic studies reveal that the enantioselectivity originates from the dynamic kinetic resolution of seleniranium ions through anion-binding catalysis.
520 $a Chapter 3 details our discovery of a squaramide-catalyzed enantioselective iodoisocyanation reaction, which represents a rare example in asymmetric intermolecular halofunctionalization of simple olefins. Kinetic studies reveal that [I(NCO)2] --1 anion is the counterion of iodonium intermediate and the dual H-bond donor catalyst aggregates in the resting state. Hammett analysis indicates that the degree of stabilization by catalyst to the iodonium intermediate accounts for both catalysis and enantioselectivity.
520 $a The reactions developed in Chapter 2 and 3 have therefore extended anion-binding catalysis to reactions involving chiral and stereochemically labile halonium and seleniranium cations. Knowledge learned in these studies will provide valuable guidance to the development of asymmetric transformations involving other chiral cationic intermediates.
590 $a School code: 0084.
650 4 $a Organic chemistry. $3 523952
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710 2 $a Harvard University. $b Chemistry and Chemical Biology. $3 2094763
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791 $a Ph.D.
792 $a 2016
793 $a English
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