PericyclicReactionI.ConceptsandprinciplesPericyclicreaction:formationofacycliccompoundanditsreverseprocessinaconcertedmanner.CHOheatCHONointermediate(ionorradical)existsintheprocess.1.Cycloadditionsheath2.Electrocyclicreactionshh3.CheletropicreactionshSO2SO2+4.SigmatropicrearrangementsOheatOCH2CH=CH2HOHCH2CH=CH25.Theene-reactionHHheatRelatedtheoriesofpericyclicreaction1.Frontierorbital-----Fukui2.Conservationoforbitalsymmetry----WoodwardandHoffmannFrontierorbitals:HOMO:thehighestoccupiedmolecularorbitalLUMO:thelowestunoccupiedmolecularorbitalCCHHHHp-bondingHOMO:LUMO:Frontierorbitalsorory1y2y3y4HOMOLUMOBondingorbitalsAnti-bondingorbitalsy1y2y3y6y5y4HOMOLUMOII.Cycloadditionh+heat+[2+2][4+2][2+2]additionHOMOLUMOSymmetryforbiddenHOMOLUMOSymmetryallowedAfterirradiationoflight[4+2]addition,Diels-AlderreactionHOMOLUMOLUMOHOMOSymmetryallowedSymmetryallowedheat+dienedienophilecisoidtransoidC(CH3)2C(CH3)3DonotreactwithdienophilesThesubstituentfactorseffectingonthereactivityoftheD-Areactiona.StericfactorRHHcrowdingCH3OOO+0oCOOOCH3CH3OOO+100oCOOOCH3100%4%b.ElectricfactorDiene:electron-releasingsubstituentsatC-1,4favorthereactionDienophile:electron-withdrawingsubstituentsfavorthereaction.+SO2PhSO2PhNa-Hgheat+CH3CH3CO2EtCO2EtCH3CH3CO2EtCO2EtApplicationsoftheDiels-Alderreaction1.Inthebuildingofsix-memberedrings+CH2=CHCHOCHOCH2=CHCOCH3COCH3PhCH=CHNO2NO2PhOOOO2.Inthebuildingofbicyclicsystems+Cl+Cl+OOOOOOO+OOOOOOOSNHareinactivetotheD-AreactionNCO2R+CO2EtCO2EtNCO2RCO2EtCO2Et3.Insynthesisofsix-memberedheterocyclesOCH3+HCCO2EtOOOCH3CO2EtCH3+CHCCl3NTsNCH3CCl3Ts+NCO2EtNCO2EtEtO2CN=NCO2Et+NONOPhPhRegiochemistryoftheD-AreactionPh+PhCO2EtCO2EtPhCO2Et+391CH3+CO2EtCH3CO2EtCH3CO2Et+70%30%CH3+CHOCH3CHOCH3CHO+59%41%usingSnCl4ascatalyst96%4%OHOMe3SiClHClMe3SiOOOMe3SiOOOH3O+OOMeMe3SiClHClMe3SiOOMeH3O+MeO2COMeCO2MeMe3SiOHCO2MeOHDanishevsky’sdieneStereochemistryoftheD-AreactionCis-addtion+CO2EtCO2EtCO2EtCO2Et+CO2EtCO2Et+CO2EtCO2EtCO2EtEtO2CSuprafacialinteractionRR'+RR'RR'+RR'Endo-addition++endoexomain+OOOOOOOOO+mainO+ONOONOOONHOOH25oC90oC90oCH