A Diversified Construction Method For Multi-substituted Furan Compounds Without Heavy Metal Participation

Dihydrofurans and furans are widely occurring as natural products with important biological activities.They also serve as important synthetic intermediates and play an irreplaceable role in organic synthesis.Therefore,many different methods for constructing these compounds have been developed.Up to date,the reported approach to synthesis of substituted dihydrofurans are as follows:(1)cyclization;(2)ring opening of cyclopropane;(3)synthesis via MCRs or tandem reaction.Methods for construction of substituted furans include:(1)cyclization;(2)MCRs;(3)conversion of biomass.Although significant progress has been made in these synthetic methods,the development of a new access to substituted dihydrofurans and furans are still of significance.In our previous work,we developed a method for installing ?-alkenyl-?-hydroxy ester compounds.The method has the advantages of mild conditions,organo-catlysis,atom-economy and environmental friendliness.Furthermore,the products,a-alkenyl-?-hydroxy esters are highly-functionized compounds,which can undergo further transformation to synthesize a series of heterocyclic compounds.We envisioned that a-alkenyl-?-hydroxy esters with a homoallylic alcohol structural unit,could undergo haloetherification to form tetrahydrofuran compounds in the presence of a halogeniunm ion X+.Elimination of hydrogen halide from the tetrahydrofuran compounds under base condition results in the formation of dihydrofurans,which can be further oxidized in the presence of DDQ.The following topics have been covered in this research work:(1)Preparation of a series of a-alkenyl-?-hydroxy esters;(2)Haloetherification of a-alkenyl-?-hydroxy esters to form the substituted tetrahydrofuran compounds in the presence of NBS;(3)Transformation of the tetrahydrofurans into 2,3-or 2,5-dihydrofurans;(4)Studies on the conversion of tetrahydrofurans,2,3-and 2,5-dihydrofurans into substituted furans.In this thesis,a convenient and divergent method for synthesis substituted tetrahydrofurans,2,3-and 2,5-dihydrofurans was developed using a-alkenyl-?-hydroxy esters as substrate.This method has some features including atom-economy,organo-catalysis,divergency,and no heavy metals pollution.