Study On Organocatalytic Asymmetric Reactions Based On Iminium Activation And Study On Heck And Suzuki Reactions Catalyzed By Thiourea-Palladium Complexes

Two projects were investigated in my dissertation. The first part was about organocatalytic asymmetric reactions based on iminium activation, the second part was on Heck and Suzuki reactions catalyzed by thiourea-palladium complex.Enantioselective organocatalysis has become a field of central importance for the asymmetric synthesis of chiral molecules. Novel modes of substrate activation have been achieved using organic catalysts that can now deliver unique, orthogonal, or complementary selectivities comparable to many established metal-catalyzed transformations. Notably, the concept of iminium catalysis, one of the youngest subfields of organocatalysis, has grown almost hand in hand with the general field of organocatalysis.In the current work, readily availableα,α-diarylprolinol salts were found to be active catalysts for the stereoselective [3+2] dipolar cycloadditions of azomethine imines withα,β-unsaturated aldehydes. The catalyst with strongly electron-withdrawing groups exhibited high stereoselectivity and catalytic activity in the cycloaddtion reactions. Variously structured enantiomerical bipyrazolidin-3-one derivatives with multiple contiguous chiral centers were smoothly prepared under mild conditions (81:19 to 98:2 exo:endo, 77-97% ee for exo product).During our continuous studies on the organocatalysis based on iminium strategy, we are interested in the undeveloped asymmetric reactions between indoles andα,β-unsaturated ketones. We found that a chiral primary amine derived from natural cinchonine was an efficient organocatalyst for the asymmetric Michael-type Friedel-Crafts alkylations of indoles andα,β-unsaturated alkyl ketones for the first time. Moderate to high enantioselectivity (47-89% ee) has been achieved.Novel organocatalysts have been designed based on multifunctional primary aminocatalysts derived from cinchona alkaloids to catalyze the first organocatalytic and highly enantioselective 1,3-dipolar cycloaddition of cyclic enones and azomethine imines (endo:exo : > 99:1, 86-95% ee). The additional hydrogen bonding interaction of catalyst and 1,3-dipole is essential for the stereocontrol. To the best of knowledge, this is the first example which involves the synergistic activation of reactants in iminium catalysis.We firstly presented the synthesis of the bulky N,N-disubstituted acyclic and cyclic bis-thiourea ligands. They acted as strong coordinating ligands for palladium and the complexes demonstrated high thermal stability. Good catalytic activity for aryl iodides and bromides in Heck and Suzuki coupling reactions was exhibited under aerobic conditions for the bis-thiourea-Pd catalysts, and high TONs and TOFs were achieved (for PhI, TONs up to 1 000 000, TOFs up to 200 000; For activated bromide, TONs up to 89 000)). Moreover, spectroscopic investigation of the bis-thiourea-Pd complexes demonstrated that the active catalyst was the chelating specie in a.1:1 ratio.We have designed and synthesized the bulky and rigid bis-thiourea ligands, and the self-supported thiourea-PdCl2 complexes were firstly prepared. They acted as efficient heterogeneous catalysts in the Suzuki reaction of aryl bromides and aryl boronic acids in neat water under aerobic conditions. Moreover, facile recovery use of the heterogeneous catalysts was demonstrated without palladium leaching.