Asymmetric Synthesis Of Functionalized Pyrano[2,3-c]pyrazolones And Benzofuro[3,2-b]pyridinones Catalyzed By NHCs

The thesis is composed of three parts:(1)N-Heterocyclic carbenes(NHCs)have been regarded as one of the ideal organocatalysts due to its unique stereoelectron properties,and have been widely used in various organic syntheses.In this context,the reactions concerning different intermediates,including ?,?-unsaturated acyl cation intermediates,vinyl enealcoholates,homoealcoholates,enealcoholates and alkynyl acylcation intermediates,which were derived from carboxylic acid ester and carboxylic acid in the presence of NHCs were summarized.(2)We have developed an efficient asymmetric [4+2] annulation of substituted acetic acid and pyrazolone derivatives of oxadiene catalyzed by NHCs.When benzoic acid was added as additive,a series of functionalized pyrano[2,3-c]pyrazolones with two continuous stereogenic centers were obtained in good yields(up to 92%)with high diastereo-(>20:1 dr)and enantioselectivities(up to 97% ee).The scale-up synthesis of pyrano[2,3-c]pyrazolones has been investigated.It has provided an efficient method for synthesis of pyrano[2,3-c]pyrazolones in a consise and mild way.(3)An efficient NHCs-catalyzed asymmetric [4+2] annulation of substituted propionic acid and azadiene derived from benzofurans for synthesis of benzofuran-[3,2-b]pyridinone derivatives were established under mild and concise reaction conditions.The products with two continuous stereogenic centers were obtained in good yield(up to 90%)with excellent diastereo-(>20:1 dr)and enantioselectivities(up to >99% ee).