Palladium-catalyzed Asymmetric [3+2] Cycloaddition Reaction Of Vinyl Epoxide With Acetylenic Acid Ester

Palladium-catalyzed asymmetric[3+2]cycloaddition reaction of vinyl three-membered ring compounds with polar unsaturated compounds has developed rapidly.Because it can efficiently construct multiple chiral centers at once,it has become an important method for synthesizing multi-substituted five-membered rings.However,this type of reaction still has some challenges to be addressed.The type of polar unsaturated compounds is mainly limited to the accumulation of double bonds,electron-deficient olefins and high-activity aldehydes,ketones,imines,so far,and only few reports have appared on the use of alkynes in the reaction.This thesis investigated the pd-catalyzed asymmetric[3+2]cycloaddition of vinyl epoxide with electron-deficient alkynes.It was found that among different types of P,N-and P,P-ligands we screened,only chiral benzylic substituted P,N ligands developed by our group are effective.By using Pd（dba）₂and（S,S）-ligand having methyl and isopropyl as substituents at benzylic position and oxazoline ring as the catalyst,we successfully achieved the asymmetric[3+2]cycloaddition reaction of vinyl epoxide and electron-deficient alkynes,affording trisubstituted dihydrofurans in 19-93%yields with 60-97%ee.A wide range of aryl substituted propiolates with electron-donating and withdrawing groups at different position of phenyl ring as well as heteroaryl and naphthyl substituted were suitable.Alkyl substituted propiolates could also be used to produce desired products in good enantioselectivities albeit the yields were little bit lower.In addition,the reaction could proceed on a gram-scale with unchanged reactivity and enantioselectivity.