From Homogeneous To Heterogeneous: Several Asymmetric Reactions Catalyzed By Organocatalysts

After enzymatic and organometallic catalysis, organocatalysis has become an important and versatile approach for effective construction of chiral products in organic chemistry. At present, many chemists are interested in organocatalysis in that the organocatalysts are easily prepared, simply handled, and being insensitive to water or air. However, one of the crucial disadvantages for organocatalysis is that the requirement for the ammount of organocatalysts in homogeneous systems is too large. One way to solve this problem is, therefore, the immobilization of organocatalysts. Base on the above consideration, this dissertation, devided into five chapters, describes our research progress on homogeneous and heterogeneous organocatalysis.In ChapterⅠ, we summarize the recent developments of organocatalysis, with the emphasis on the applications of sulfones and maleimides in organocatalysis. The Chapter I is ended with the survey on the immobilization of organocatalysts over magnetic nanoparticles for applications in heterogeneous catalysis.In ChapterⅡ, our research on the asymmetric Michael addition of p-toluene sulfonylacetonitrile to a,β-unsaturated aldehydes is introduced. Moderate yields and good ee values are obtained with the utilization of Jφrgensen-Hayashi catalyst. However, the reaction does not work when a, P-unsaturated aldehydes are substituted by aryl groups.In Chapter III, we describe our research on the asymmetric Michael addtion of ethyl phenylcyanoacetate to maleimides catalyzed by cinchona alkaloids. Via this reaction, a chiral all-carbon quaternary stereogenic center is constructed with good yields and moderate ee values.In Chapter IV, the immobilization of Jorgensen-Hayashi catalyst on magnetic nanoparticles of Fe3O4 was performed and further application of the immobilized organocatalyst was achieved in the asymmetric Michael addition of aldehydes to nitrostyrenes. Good yields and ee values are obtained in this heterogeneous system.In Chapter V,, CBS catalyst (Corey, Bakshi, and Shibata catalyst) was immobilized onto magnetic nanoparticles of Fe3O4. Unfortunately, when the immobilized organocatalyst was used for reducing achiral ketones, low ee values were obtained.