Showing papers by "Ji-Woong Lee published in 2010"

Toward understanding the origin of positive effects of ionic liquids on catalysis: formation of more reactive catalysts and stabilization of reactive intermediates and transition states in ionic liquids.

Abstract: Over the past decade, ionic liquids have received a great deal of attention as a new means for catalyst immobilization. Large numbers of catalysts having polar or ionic character have been successfully immobilized in ionic liquids, thus allowing their recovery and recycling. However, catalyst immobilization is not the only benefit of ionic liquids in catalysis, of greater importance are the positive effects of ionic liquids on catalytic rates. In this Account, we highlight our work in elucidating the origin of the accelerating effects of ionic liquids in a range of catalytic reactions. Lewis acidic metal triflates often become much more reactive in ionic liquids containing noncoordinating anions as a result of "anion exchange." Consequently, the more electrophilic Lewis acidic species generated in situ accelerate the catalytic reactions dramatically. In some cases, highly reactive intermediates, such as vinyl cations, arenium cations, oxygen radical anions, and so forth, can be stabilized in the presence of ionic liquids, thus increasing the reactivity and selectivity of the reactions. Concerted processes such as S(N)2 and Diels-Alder reactions can also be accelerated through the cooperative activation of both the nucleophile and the electrophile by ionic liquids. In transition metal-catalyzed reactions, certain catalytically active oxidation states can be stabilized in ionic liquids against deactivation to catalytically inactive species. Thus it is clear that gaining an understanding of the origin of these "positive ionic liquid effects" is highly important, not only for predicting the effects of ionic liquids on other organic reactions but also for designing new catalytic reactions. Ionic liquids, by virtue of (typically) having a synthetically accessible carbon backbone, are amenable to tailoring by the organic chemist. Accordingly, their molecular structures can be subtly varied to give "tunable" properties, which can then be used to rationally examine the fundamental reasons that they accelerate catalyzed reactions. Although the origins of enhanced catalytic rates by ionic liquids have been elucidated in many areas, other undiscovered ionic liquid phenomena remain to be unearthed. Developing a better understanding of these modularly tunable liquid salts will foster new discoveries of catalytic reactions that are accelerated by ionic liquids as solvents or additives.

A chiral-anion generator: application to catalytic desilylative kinetic resolution of silyl-protected secondary alcohols.

Abstract: The resolution can be efficiently achieved with KF in the presence of a potassium complex of BPE, generated in situ.

Self‐Association‐Free Dimeric Cinchona Alkaloid Organocatalysts: Unprecedented Catalytic Activity, Enantioselectivity and Catalyst Recyclability in Dynamic Kinetic Resolution of Racemic Azlactones.

Abstract: Self-association-free, bifunctional, squaramide-based dimeric cinchona alkaloid organocatalysts show unprecedented catalytic activity, enantioselectivity and catalyst recyclability in the dynamic kinetic resolution (DKR) reaction of a broad range of racemic azlactones.

Cinchona-based bifucntional organocatalysts and method for preparing chiral hemiesters by asymmetric ring opening reaction of meso-cyclic acid anhydrides using the same

Abstract: PURPOSE: A method for synthesizing bifunctional cinchona alkaloid catalyst is provided to ensure low toxicity, and chemical stability, and synthesize chiral hemiester having various structures in a short time. CONSTITUTION: A bifunctional cinchona alkaloid catalyst is denoted by chemical formula 1 or 2. A chiral hemiester is produced by reacting a prochiral or meso-cyclic acid anhydride with nucleophile in organic solvent under the presence of the bifunctional cinchona alkaloid catalyst. The nucleophile is alcohol or thiol. The organic solvent is dimethoxyethane, ethylvinyl ether, methyl t-butyl ether, diethyl ether, diisopropyl ether, tetra hydro furan or dioxane.

Bifunctional organic chiral catalyst compound with superior stereoselectivity, method for preparing same, and method for preparing chiral amino acids from azlactone using same

Abstract: The present invention relates to a method for obtaining chiral amino acid esters having high stereoselectivity from racemic or chiral azlactone, and provides a derivatized bifunctional organic chiral catalyst compound used in the method, and a method for preparing the compound. Conventional preparation methods have the drawbacks of a long reaction period at a low temperature being required to obtain N-acyl amino acid esters having a high enantioselectivity, and the optical selectivity of the obtained compound is not sufficient for industrialization. The catalyst compound according to the present invention can be easily synthesized from cinchona alkaloids. The present invention enables N-acyl amino acid esters having a high enantioselectivity to be obtained in a remarkably economical and simple manner, and enables various (R)-type N-acyl amino acid esters not found in nature to be prepared with high optical purity, and can thus be valuably utilized as a technique for industrialization.

Games with non-probabilistic uncertainty

Abstract: The thesis studies games with non-probabilistic uncertainty about some parameters that affect the rewards of the players. The goal is to understand whether players should be optimistic or pessimistic in such situations. The first chapter provides a brief overview of the standard solution concepts in Game Theory. The second chapter proposes a model where the players are strategic in choosing their attitude (degree of optimism), instead of having an intrinsic risk aversion. The idea is that Alice may be able to take advantage of Bob's pessimism, in which case Bob should not be pessimistic. The chapter presents a few examples of two-player non-cooperative games where the agents have a dominant attitude (e.g., optimism), regardless of the unknown private information of the opponent. The chapter also analyses a Cournot duopoly game where each firm has confidential knowledge of its production cost. In the symmetric case, it is shown that pessimism is never a dominant attitude. Finally, the chapter defines a robust attitude and the price of uncertainty, and analyzes them in the Cournot duopoly game. The third chapter studies a simple wireless network with two relay nodes that cooperate to forward information to a common destination. For a range of success probabilities, only the node with the largest success probability should relay packets to avoid collisions at the destination. However, the success probability of a node is known initially only to that node. To improve the performance of the network, the nodes exchange link state messages through a control channel that is not fully reliable. The chapter studies a protocol where each node tries to protect the performance against the worst possible choice of the other node. The performance of that protocol does not converge as the relays exchange more and more link state messages. Essentially, the relay nodes use an excess of caution. The chapter studies another protocol where each relay node ignores the possible states of knowledge of the other node. The throughput of this less cautious protocol converges to the maximum possible value.

Optimism in games with non-probabilistic uncertainty

Abstract: The paper studies one-shot two-player games with non-Bayesian uncertainty. The players have an attitude that ranges from optimism to pessimism in the face of uncertainty. Given the attitudes, each player forms a belief about the set of possible strategies of the other player. If these beliefs are consistent, one says that they form an uncertainty equilibrium. One then considers a two-phase game where the players first choose their attitude and then play the resulting game. The paper illustrates these notions with a number of games where the approach provides a new insight into the plausible strategies of the players.