Chiral Complexes Designed to Catalyzed Organic Reactions

点击翻译按钮获取中文摘要

This program is dedicated to the development and elucidation of new principles for stereoselective catalysis, and in the application of those principles to the invention of practical synthetic methods for the preparation of chiral, bioactive compounds. This renewal application is focused on two distinct approaches to the generation and stereocontrolled reaction of highly electrophilic intermediates. Each of the proposed reaction manifolds is based on firm mechanistic hypotheses gleaned from extensive preliminary investigations. The first involves the application of precisely designed chiral ureas, thioureas, and squaramides to catalyze enantioselective reactions via ion-pair intermediates. These dual hydrogen-bond donors can abstract or bind weakly basic anions, such as halides, sulfonates, and carboxylates, to generate chiral ion pairs that remain tightly associated during subsequent selectivity-determining reactions of the prochiral cations. We discovered that the combination of hydrogen-bond donors with achiral Lewis or Brønsted acids generates highly reactive complexes that can promote activation and enantioselective reactions of weakly electrophilic substrates. This new principle is directed to creative new applications including the enantioselective multi-component synthesis of amines from carbonyl compounds and to the asymmetric ring opening of oxetanes. The principle of anion-abstraction catalysis is also applied in a new way to the promotion of enantioselective boronate rearrangements, through a novel chiral recognition mechanism involving discrimination of enantiotopic leaving groups. The boronate rearrangement methodology provides a general approach to the systematic construction of trisubstituted stereocenters from readily available organoboron derivatives. The second distinct approach involves the oxidative fluorofunctionalization of alkenes using hypervalent iodine catalysis. We have discovered that simple C2-symmetric aryl iodides catalyze enantioselective difluorination of simple alkenes via a multistep mechanism involving a highly reactive fluoroalkyl iodane intermediate. That intermediate can be intercepted in a variety of intra- or intermolecular reactions, leading to novel, 1,1-, 1,2-, and 1,3-fluorofunctionalized products in highly enantioenriched form. Efforts are directed toward the mechanistic elucidation of the new reactions, and to their practical enablement through the use of practical fluoride sources.