A Journey in Brønsted Acid Catalysis: From Organic Brønsted Acids to Lewis Acid Assisted Brønsted Acids
소속 :
연사 : Prof. Cheon Cheol Hong (Korea University, Department of Chemistry )
일시 : 2012-04-12 17:00 ~
장소 : 500동 목암홀
일 시 : 2012년 4월 12일 오후 5시
장 소 : 500동 목암홀
-Abstract-
We have witnessed that Brønsted acid catalysis has been growing extremely rapidly over the past decade in various organic reactions. Several classes of new Brønsted acids have been developed and successfully demonstrated their usefulness in a variety of reactions. However, the use of Brønsted acid catalysis has been a little bit limited to more reactive substrates compared to that of Lewis acid catalysis presumably due to their lower reactivity. Thus, it is highly desirable to develop more strong Brønsted acids to extend the use of Brønsted acids to more general substrates.
In this regard, we have employed several different approaches to improve the reactivity of Brønsted acids. The first approach to improve reactivity of Brønsted acids was introduction of a more polarizable atom in Brønsted acid. In this approach, N-triflyl thio- and seleno- phosphoramides 1a-b have been developed and successfully applied to enantioselective protonation and Mukaiyama aldol reaction. Second approach was development of a new Brønsted acid derived from a new catalophore. Based on this idea, new strong Brønsted acids 2a-c have been developed from squaric acid moiety as a new catalophore. These Brønsted acids could be applied to various carbon-carbon bond formation reactions, such as Mukaiyama aldol, Mukaiyama Michael, Hosomi-Sakurai, and carbonyl ene reactions. The third approach to increase acidity was Lewis acid assistance, so called Lewis acid assisted Brønsted acid (LBA). In this approach, two different types of LBAs 3a-b have been developed: one is LBA 3a from La(OTf)3 and a chiral alcohol in the presence of achiral alcohol, and the other LBA 3b was developed via σ-complexation of cationic chiral gold complex with alcohol. The usefulness of these LBAs 3a-b was demonstrated in catalytic asymmetric protonation reactions. In particular, LBA 3b could be applied to the first asymmetric protonation reaction of acyclic silyl enol ethers. In this presentation, the recent research progress in the development of strong Brønsted acids and their application to organic reactions will be discussed.
장 소 : 500동 목암홀
-Abstract-
We have witnessed that Brønsted acid catalysis has been growing extremely rapidly over the past decade in various organic reactions. Several classes of new Brønsted acids have been developed and successfully demonstrated their usefulness in a variety of reactions. However, the use of Brønsted acid catalysis has been a little bit limited to more reactive substrates compared to that of Lewis acid catalysis presumably due to their lower reactivity. Thus, it is highly desirable to develop more strong Brønsted acids to extend the use of Brønsted acids to more general substrates.
In this regard, we have employed several different approaches to improve the reactivity of Brønsted acids. The first approach to improve reactivity of Brønsted acids was introduction of a more polarizable atom in Brønsted acid. In this approach, N-triflyl thio- and seleno- phosphoramides 1a-b have been developed and successfully applied to enantioselective protonation and Mukaiyama aldol reaction. Second approach was development of a new Brønsted acid derived from a new catalophore. Based on this idea, new strong Brønsted acids 2a-c have been developed from squaric acid moiety as a new catalophore. These Brønsted acids could be applied to various carbon-carbon bond formation reactions, such as Mukaiyama aldol, Mukaiyama Michael, Hosomi-Sakurai, and carbonyl ene reactions. The third approach to increase acidity was Lewis acid assistance, so called Lewis acid assisted Brønsted acid (LBA). In this approach, two different types of LBAs 3a-b have been developed: one is LBA 3a from La(OTf)3 and a chiral alcohol in the presence of achiral alcohol, and the other LBA 3b was developed via σ-complexation of cationic chiral gold complex with alcohol. The usefulness of these LBAs 3a-b was demonstrated in catalytic asymmetric protonation reactions. In particular, LBA 3b could be applied to the first asymmetric protonation reaction of acyclic silyl enol ethers. In this presentation, the recent research progress in the development of strong Brønsted acids and their application to organic reactions will be discussed.
