Study Based On The Cyclization Reactions Of Oxiranes And Conjugated Enyes

Cyclic compounds are present in many natural products and medicinal molecules with biological activity. Therefor, it is very important to develop some novel and efficient cyclization reactions for synthesis of natural products and construction of a wide range of molecules with potential biological activity. This thesis mainly consist of two parts:(1) cyclization of oxirane derivatives and their mechanism study,(2) cyclization of electron-deficient enynes.In the first part, we established for the first time an efficient approach to carbonyl ylides which trapped with aldehydes by Lewis acid catalyzed chemoselective C-C bond hetorolysis of activated oxiranes. Initially, We synthesized various rationally designed aryl oxiranyl diketones. After numerous attempts, we found that the reaction of aryl oxiranyl diketones and aldehydes proceeded smoothly to afford highly substituted1,3-dioxolanes with excellent diasteroselectivity and chemoselectivity under the catalysis of Yb(OTf)3. When the activated groups were switched to dicarboxylates, we achieved chemodivergent cycloaddtion reactions of activated oxiranes with aldehydes. The reaction worked well to produce the corresponding cycloadduts with C-O bond cleavage of oxiranes under the catalysis of Sn(OTf)2, however, the expected1,3-dioxolanes with C-C bond cleavage of oxiranes were obtained when the Ni(ClO4)2was involved. Based on a series of control experiments and computational study, a mechanism was proposed. Finally, the cycloaddition reactions of styrenyl epoxides and aryl oxiranyl dicarboxylates catalyzed by Ni(ClO4)2was also achieved in mild conditions. It is noteworthy that dual activation of both the two reagents is the key to this reaction.In the last part, we developed a novel tandem Michael addition and ylide annulation of a crotonate-derived sulfur ylide with readily available electron-deficient enynes catalyzed by Et3N, which provide a rapid, efficient and selective route to multi-functionalized4-alkylidenebicyclo-[3.1.0]hex-2-enes. We also discovered an unexpected phosphine-catalyzed regio-and diastereoselective [4+1] annulation reaction of modified Morita-Baylis-Hillman adducts with activated enones to afford multifunctionalized dihydrofurans. In these annulations, Morita-Baylis-Hillman carbonates act as the one carbon unit, which is distinguished from Lu et al. reported modified allylic compounds as the three carbon units in [3+n] annulation reactions.