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1、WelcometoAdvancedOrganicChemistryThewholeartofteachingisonlytheartofawakeningthenaturalcuriosityofyoungmindsforthepurposeofsatisfyingitafterwards.AnUnexpectedRoleofaTraceAmountofWaterinCatalyzingProtonTransferinPhosphine-Catalyzed(3+2)CycloadditionofAllenoatesandAlkenesYuanzh
2、iXia,YongLiang,YuanyuanChen,MingWang,LeiJiao,FengHuang,SongLiu,YahongLi,andZhi-XiangYu*J.Am.Chem.Soc.,2007,129(12),3470-3471zwitterionicintermediatezwitterionicintermediateTheLu(3+2)cycloadditionisalsoefficientforthesynthesisoffive-memberedheterocyclesifiminesareusedasdipolar
3、ophiles.ThroughelegantworkinthegroupsofZhangandFu,asymmetricversionsoftheLu(3+2)cycloadditionhavebeendeveloped.ApplicationsoftheLu(3+2)cycloadditiontothetotalsynthesisofnaturalproductshavealsobeendocumentedbyLu,Krische,andPyne,respectively.Furtherelegantevelopmentsandextensio
4、nsofthechemistryofallene-PR3havebeenwidelypursuedbymanyothergroupsaswell.Inconclusion,theLu(3+2)cycloadditionhasbeeninvestigatedwithjointforcesofcomputationandexperiment.Theformationofa1,3-dipoleisslightlyexothermic,andthesubsequent(3+2)cycloadditionisastepwiseprocesswithanac
5、tivationfreeenergyof28.3kcal/mol.Thegenerallyacceptedintramolecular[1,2]protonshiftintheLureactionisnotpossibleowingtotheveryhighactivationbarrierof39.6kcal/molrequiredforthisprocess.Calculationsandexperimentsrevealedthatwaterassiststhisprocesswithanactivationfreeenergyof7.7k
6、cal/mol.ThediscoveryofthecatalyticroleofatraceamountofwaterintheLureactionsuggeststhatatraceamountofwatercouldalsoactasacatalystinsomeother“anhydrous”reactionsinvolving[1,2]or[1,n]protonshifts.IntermediateswithChargedCarbonAtoms(+1)Ammonium,phosphonium,sulfonium,etc.CH+H++2CH
7、3碳正离子（carbocation,carboniumcarboniumion,positivecarbonion,ions）ò碳正离子：一类碳上只带有六个电子的活泼中间体CH3RCH2R2CHR3C1o2o3osp2杂化甲基碳伯碳正仲碳正叔碳正平面型正离子离子离子离子¾碳正离子一般无法分离得到，可通过实验方法捕获：(CH3)3CF+SbF5(CH3)3CSbF6超酸可通过核磁共振观察到TheformationofalkylcationsevenfromalkanesMe3CH+SbF5/FSO3HH2+MeC+SbFFSO-353Myworko
8、nlong-livedcarbocationsdatesbacktothelate1950satDowandresultedinthef
