高等有机化学-反应机理

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1、高等有机化学——反应机理第四课周环反应1、基础知识Apericyclicreactionisareactioninwhichbondsareformedorbrokenattheterminiofoneormoreconjugatedsystems.Theelectronsmovearoundinacircle,allbondsaremadeandbrokensimultaneously,andnointermediatesintervene.TypicalreactionsRegioselectivityStereoselectivityStereo

2、specificity4.1.1ClassesofPericyclicReactionsElectrocyclicreactions(ringopeningsorringclosings),CycloadditionsSigmatropicrearrangementsEnereactions.ElectrocyclicreactionsCycloadditionsCheletropicreactionsCycloadditionsSigmatropicrearrangementsSigmatropicrearrangementsSigmatropicr

3、earrangementsEneReaction四种周环反应总结立体专一性PolyeneMOsWoodward–HoffmannrulesPolyeneMOsPolyeneMOsPolyeneMOs2、电环化反应2.1、典型反应2.1、典型反应2.1、典型反应2.1、典型反应练习4.12.1、典型反应2.1、Favorskiirearrangement2.1、Favorskiirearrangement练习练习4.2.2Stereospecificity1,3,5-hexatrienes偶——热——顺奇——热——反偶——光——反奇——光——顺TheWo

4、odward–Hoffmannrulesapplyonlytoconcerted,pericyclicreactions.AreactioncanbeforcedtoproceedthroughthehigherenergyTSifthelowerenergyoneisraisedprohibitivelyhighinenergybygeometricconstraints.4.2.3Stereoselectivity4.3Cycloadditions4.3.1TypicalReactions4.3.1.1TheDiels–AlderReactionM

5、ostDiels–Alderreactionsoccurwithwhatiscallednormalelectron-demand,inwhichanelectron-rich(nucleophilic)dienereactswithanelectronpoor(electrophilic)dienophile.Normalelectron-demandDiels–Alderreactions用前线轨道理论解释反应活性炔烃的D-A反应活性低(Aldrin)VeryelectronpoordienescanundergoDiels–Alderreacti

6、onswithelectronrichdienophilesintheinverseelectron-demandDiels–Alderreaction.ThedominantinteractionintheTSofinverseelectron-demandDiels–AlderreactionsisbetweentheLUMOdieneandtheHOMOdienophile.Inverseelectron-demandDiels–Alderreaction4.3.1.2OtherCycloadditions（1）[3+2]Cycloadditio

7、ns(加入Me2S使过氧化物还原为醛)Paterno–Büchireaction（2）[2+2]Cycloadditions（胸腺嘧啶）（导致皮肤癌）Wittigreaction（3）[4+1]Retro-cycloadditions4.3.2Regioselectivity定位规则：Diels–Alderreactionsproceedtoputthemostelectrondonatingsubstituentonthedieneandthemostelectronwithdrawingsubstituentonthedienophileeithe

8、r“ortho”or“para”tooneanother.(1)Normalelectron-