Application Of Samarium Reagents And Baylis-Hillman Adducts In The Organic Reactions

The dissertation consists of three chapters. In the first one, samarium reagents promoted organic reactions and the application of Baylis-Hillman reaction in organic synthesis are briefly described. The second one describes the reductive elimination reactions promoted by samarium reagents. The third chapter makes a detailed study of a variety of stereoselective transformation based on Baylis-Hillman adducts.Chapter one introduces the usual types of samarium reagents, and the representative usage in organic synthesis of samarium(II) iodide and metallic samarium is discussed. In general, activation is needed in the direct use of metallic samarium. Then the origin of Baylis-Hillman reaction is mentioned together with the proceeding of Baylis-Hillman reaction catalyzed by various catalysts. Finally, the application of Baylis-Hillman adducts is also briefly reviewed.Chapter two describes a new strategy to form carbon-carbon double bonds via the reductive elimination reaction promoted by samarium diiodide. The experimental results show that the SmI₂-mediated reduction elimination of trichlomethyl carbinols leads to the formation of the important intermediate vinyl dichlorides. The advantages of this method are the direct elimination of hydroxyl group from the substrate, which have important synthetic value. In addition, structurally similar substrates chloral amide also experience the elimination reaction promoted by samariunm diiodide to give N-(2,2-dichlorovinyl)amides in excellent yields. This novel reaction proceeds readily within a few minutes at room temperature.Chapter three focuses on the application of the Baylis-Hillman adduct in organic synthesis and some new exploration was made. In part one the direct elimination of hydroxy group from Baylis-Hillman adducts were investigated promoted by SmI₂ in a solution of THE The present method was found to be a temperature-controlled selective reaction for the first time: the ratio of two products could be tuned by simple temperature changes. While the formation of reductive product a-methylcinnamic ester predominates under reflux, lower temperature favors the tramsformation towardscoupling product 1,5-hexadiene. In part two we also made detailed study on the reduction of Baylis-Hillman acetates by the direct use of metallic samarium and catalytic amount of iodides. It was found that the transformation could proceed without the protection of nitrogen atmosphere and have potential for large-scale preparation. To our surprise, when the amount of iodide was added to 1:1 ratio with samarium, another different reaction occurred to give the iodination product (2Z)-2-(iodomethyl)alk-2-enoates in high yields. In part three we developed another highly efficient method for the synthesis of allylic iodide. Promoted by the TMSCl/Nal system the Baylis-Hillman adducts was coverted to allylic iodide with high stereoselectivy and the present method proceeded readily at room temperature. Further investigation showed that the TCT/DMF system could also be used for the allylation of Baylis-Hillman adducts. In the last part the nucleophilic reaction of Baylis-Hillman adducts with imidazole was attempted to synthesize a variety of new AT-substituted imidazole derivatives. It was found that water have obvious acceleration effect on this substitution reaction. Subsequently, we paid much attention to another transformation after the addition of DABCO to the above reaction system and another Sn2 type AMmidazole derivatives were obtained. In fact, total process was indeed tandem Sn2'- Sn2' pathway to give Sn2 product. Similarly, benzotriazole was also tried in this substitution reaction in the presence of DABCO and the Sn2 type iV-substituted benzotriazoles were isolated in high yields. These benzotriazole derivatives were stable and the condition was also mild. As a result, these special compounds had great potential to be used in pharmaceutical industry.