Organocatalytic Synthesis Of Triazole,Isoxazole And Asymmetric Synthesis Of Chromene Derivatives

Organocatalysis is an increasingly active area of organic synthesis in recent years.Compared with the traditional metal catalysis,enzyme catalysis etc.,its raw materials are simple and easily made,it's easily separated from the product,more importantly,the reaction system is harmless to the body without metal residue,and this is consistent with the current promoting environmentally friendly green chemistry requirements.So,in this thesis,the organic synthesis methods for three kinds of heterocyclic compounds are described in detail in three parts.Part I: A [3+2] reaction between b-keto amides and azides was developed and 1,4,5-trisubstituted 1,2,3-triazoles were obtained.In this part,the reaction proceeds efficiently in the presence of a simple and cheap catalyst at room temperature.The reaction of ?-keto amide with catalyst generates the enolate,after optional conditions and the scope of substrates,1,4,5-trisubstituted 1,2,3-triazoles were obtained in high yields and regioselectivities.Part II: A [3+2] reaction between ?-functionalized ketones and nitrile oxides was designed and 3,4,5-trisubstituted isoxazoles were obtained.In this part,there is no report on organocatalytic 1,3-dipolar cycloaddition reactions to achieve 3,4,5-trisubstituted isoxazoles so far.Besides,the catalysts and substrates are easy to buy and synthesize,and this reaction could generate various 3,4,5-trisubstituted isoxazoles in high yields and regioselectivities.Part III: Asymmetric synthesis of chromene skeletons via organocatalytic domino reactions of para-quinone methide(p-QMs)with ?-functionalized ketone was devised.ortho-Quinone methides(o-QMs)are in stiu generated under the hydrogen bond of bifunctional catalyst and p-QMs.Finally,the chiral chromenes were synthesized in high yields and enantioselectivities.