The Application In The Construction Of Dihydro- Furans Derivatives Based On The Design Of Intramolecular Trapping Of Oxonium Ylides

2,5-dihydrofuran, a common structural motif in many bioactive natural products, has high value in synthetic chemistry. However, it’s a formidable task for us to construct polysubstituted 2,5-dihydrofuran derivatives with a quaternary center in high enantioselectivity using simple and available starting materials.In recent years, our group focuses on the development of active intermediate-trapping process that employs electrophiles to trap the active ylides or zwitterionic intermediates, which are generated by the attack of metal carbenes to the lone electron pairs of the nucleophiles. Besides the application of multi-component cascade reactions based on intermolecular trapping process, we find intramolecular trapping strategy makes less active electrophiles succeed in the ylide trapping reaction. This new strategy provides a facile method for the construction of polyfunctional heterocycles. Combined our previous works with this strategy, we achieve the intramolecular trapping of oxonium ylides and finally obtained cycloaddition product, 2,5-dihydrofuran derivative.In this thesis, the first part introduces metal carbenoids, diazo compounds, and typical reports of heterocycle’s synthesis via the trapping of active intermediates. Based on the research background, we propose our project ideas.Palladium (Ⅱ)-catalyzed formal [4+1] cycloaddition reactions to form 2, 5-dihydrofuran derivatives is described in the second part. We find the reaction of diazoacetates and aryl propargyl alcohols can undergo diverse pathways via the choice of different metal catalysts. Surprisingly, when allyl palladium (Ⅱ) chloride is used as the catalyst,2,5-dihydrofuran derivatives are afforded as the dominant product with relatively high yield. This is the first example of trapping the oxonium ylides with internal alkynes. Additionally, dihydrofurans can undergo diffenrent transformations to obtain useful derivatives including the highly substituted butenolides.In the third part, we investigate the highly enantioselective carbene transfer reaction by a bifunctional silver catalyst. We make efforts to achieve the asymmetric synthesis of chiral dihydrofurans on the basis of previous research. After screening different metal salts and chiral ligands, we find the common used catalyst system, AgSbF6-BINAP complex can be successfully applied to the enantiocontrol of formal [4+1] cycloaddition, which affords chiral 2,5-dihydrofuran derivatives up to 94% ee. It is the first time that highly enantioselective silver carbene transfer reaction has been achieved. We also conduct further mechanism study on the bifunctional silver catalysis.In conclusion, we provide a new example for the construction of heterocycles using the intramolecular trapping of oxonium ylides. We also find an effective way to the synthesis of polysubstituted 2,5-dihydrofuran derivatives with a quaternary center in high enantioselectivity.