高等有機(jī)化學(xué)-反應(yīng)機(jī)理-6課件

高等有機(jī)化學(xué)——反應(yīng)機(jī)理第四課周環(huán)反應(yīng)1、基礎(chǔ)知識(shí)

Apericyclicreactionisareactioninwhichbondsareformedorbrokenattheterminiofoneormoreconjugatedsystems.Theelectronsmovearoundinacircle,allbondsaremadeandbrokensimultaneously,andnointermediatesintervene.TypicalreactionsRegioselectivityStereoselectivityStereospecificityElectrocyclicreactionsCycloadditionsCheletropicreactionsCycloadditionsSigmatropicrearrangementsSigmatropicrearrangementsEneReaction立體專(zhuān)一性PolyeneMOsWoodward–HoffmannrulesPolyeneMOsPolyeneMOs2、電環(huán)化反應(yīng)2.1、典型反應(yīng)2.1、典型反應(yīng)2.1、典型反應(yīng)練習(xí)4.12.1、Favorskiirearrangement2.1、Favorskiirearrangement練習(xí)4.2.2Stereospecificity1,3,5-hexatrienes偶——熱——順奇——熱——反偶——光——反奇——光——順

TheWoodward–Hoffmannrulesapplyonlytoconcerted,pericyclicreactions.AreactioncanbeforcedtoproceedthroughthehigherenergyTSifthelowerenergyoneisraisedprohibitivelyhighinenergybygeometricconstraints.4.2.3Stereoselectivity4.3Cycloadditions4.3.1TypicalReactions4.3.1.1TheDiels–AlderReactionMostDiels–Alderreactionsoccurwithwhatiscallednormalelectron-demand,inwhichanelectron-rich(nucleophilic)diene

reactswithanelectronpoor(electrophilic)dienophile.Normalelectron-demandDiels–Alderreactions用前線軌道理論解釋反應(yīng)活性炔烴的D-A反應(yīng)活性低(Aldrin)VeryelectronpoordienescanundergoDiels–Alderreactionswithelectronrichdienophilesintheinverseelectron-demand

Diels–Alderreaction.ThedominantinteractionintheTSofinverseelectron-demandDiels–AlderreactionsisbetweentheLUMOdieneandtheHOMOdienophile.Inverseelectron-demandDiels–Alderreaction4.3.1.2OtherCycloadditions（1）[3+2]Cycloadditions(加入Me2S使過(guò)氧化物還原為醛)Paterno–Büchireaction（2）[2+2]Cycloadditions（胸腺嘧啶）（導(dǎo)致皮膚癌）Wittigreaction（3）[4+1]Retro-cycloadditions4.3.2Regioselectivity定位規(guī)則：Diels–Alderreactionsproceedtoputthemostelectrondonatingsubstituentonthedieneandthemostelectronwithdrawingsubstituentonthedienophileeither“ortho”or“para”tooneanother.(1)Normalelectron-demandDiels–Alderreactions(2)Reverseelectron-demandDiels–Alderreactions[4+2]環(huán)加成反應(yīng)的立體定向性[3+2]環(huán)加成反應(yīng)的立體定向性