N-Heterocyclic Carbene-Catalyzed Enantioselective Synthesis Of Benzofuran-fused Dihydropyranones

N-Heterocyclic carbene(NHC),profiting by its unique structure,has been developed as one of the most powerful organocatalysts.It can catalyze a variety of reactions under mild conditions.N-Heterocyclic carbene has been widely used in organic synthesis,especially the asymmetric synthesis.It provides a new way to synthesize cyclic compound,in particularly the heterocyclic compounds.In this thesis,a series of chiral compounds containing benzofuran fused dihydropyrone structure were constructed by aurones and a-chloroaldehyde with the catalysis of N-Heterocyclic carbene.The strcture of benzofuran fused dihydropyrone has been widely found in many natural products,chemical materials and drug molecules.However,the synthesis of this structure has rarely been reported.In this paper,the N-Heterocyclic carbene-catalyzed[4 + 2]annulation of chloroaldehydes and aurones was developed,giving the highly enantioselective benzofuran-fused dihydropyranones.In this study,we have conducted a large number of screenings on the reaction conditions including the types of catalysts in the reaction system,catalyst loading,organic bases and inorganic bases,solvents for reaction and reaction temperatures and determined the optimal conditions of the reaction through the reaction yield,ee.and dr.The two initial substrates were extended under these conditions,it was found that the reaction has good substrate applicability.Moreover,a series of benzofuran fused dihydrogen was obtained with moderate to excellent yields and good ee and dr.This research is beneficial to thestudy of the biological activity and drug value of the compounds and widen the application of chloroaldehydes in the N-Heterocyclic carbene chemistry.At the end of this thesis,the possible mechanism of the reaction was proposed and the relative configuration of the compound was defined by the NOE spectrum.