Study On Cascade Reactions Triggered By Intramolecular Cycloisomerization Of Alkyne And Carbonyl Functionalities

Isochromenyliums are a unique type of highly reactive intermediates, which were involved in many diverse reactions and applied in constructing the key skeleton of natural products. Our research group has studied the synthesis of stable isochromenylium salts and the corresponding enantioselective cooperative binary catalytic cascade reactions, and made great progress. Considering potential applications of the isochromenyliums in organic synthesis, it is of value to further study the scope of stable isochromenylium salts and the established enantioselective cascade reactions. Based on our achievements and interests in this field, rational designs were proposed and careful explorations were attempted and discussed in this thesis. The major discoveries in this work include:First, a Br(?)nsted acid-promoted dimerization reaction of o-alkynylbenzaldehydes was developed in expanding the scope of stable isochromenylium salts. This reaction was further applied into a cascade methodology for one-step synthesis of various Kagan’s ethers through the dimerization of o-alkynylbenzaldehydes bearing electron-withdrawing groups or weakly electron-donating groups. These products could be transformed into the Kagan ether’s analogues through simple transformations. Second, a cooperative binary catalytic asymmetric cascade reaction including an intramolecular alkyne/carbonyl cycloisomerization and an oxa Diels-Alder reaction was developed. Excellent enantioselectivity could be achieved under the optimized reaction conditions. To the best of our knowledge, this is the first cascade asymmetric methodology applying asymmetric counteranion-directed catalysis (ACDC) principles.Our new findings and achievements from this work provide a solid foundation for further study of the chemistry of cyclic oxoniums.