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1、Pure&Appl.Chern.,Vol.66,No.7,pp.1557-1564,1994.PrintedinGreatBritain.01994IUPACNovelLewisacidcatalysisinorganicsynthesisKeisukeSuzukiDepartmentofChemistry,KeioUniversity,3-14-1Hiyoshi,Yokohama223,JapanAbstract:CationiczirconoceneorhafnocenecomplexesserveasanovelclassofLewisacidwithuniquereactivities
2、,whicharetobeexploitedinorganicsynthesis.Fourcategoriesofreactivitiesarediscussed,thatis,(A)C-Fbondactivation/cleavage,(B)Coordinativeactivationofetherlinkages,(C)Carbonylactivation,and(D)C-0bondcleavageviazirconocenealkoxide.IntroductionLewisacid-promotedreactionsarebecomingofincreasingimportancein
3、currentorganicsynthesis(ref.1).AgeneralideaforsuchreactionsisshowninScheme1.InitialcoordinationofaLewisacidoccurstothebasicsiteofthesubstrate.Whentheactivationlevelreachedhighenough,theionizationoccurstogenerateacationicspecies,whichisrevertedtothestartingmaterialortrappedbyanucleophiletogivetheprod
4、uct.TheLewisacidplaysthekeyroletodeterminetheoverallreactionpathbycontrollingthegenerationandtrappingofthecationicspecies.Ifthesubstratehasmanybasicfunctionalities,specificityisrequiredforthisacid-baseinteractioninthatoneparticularfunctionalityistobeactivatedbutnottheothers.TheLewisaciddecidesalsoth
5、enatureofthecationicspeciesgenerated,anionpairoralooselyboundcovalentspeciesorsomewherein-between.nActivationCI-LIReversionScheme1Inthiscontext,wehaverecentlybeenfindingthatthecationiczirconoceneorhafnocenecomplexesbehaveasanewclassofLewisacidwithuniquereactivities,whichwouldbeusefulinorganicsynthes
6、is.Fourcategories(A-D)ofthereactivitiesofsuchcationiccomplexesarediscussed.AC-FbondActivarionofcCurbony1DC-0BondClwwgeEther.LinkngeActiwtionClenwigrResultsandDiscussion(A)TheC-FbondactivatiodcleavageSomeyearsago.wefoundthatthecombinationofhafnocenedichlorideandsilverperchlorateactsasapowerfulactivat
7、orofglycosylfluoride(ref.2).Scheme2showsourreasoningfortheoriginofthe15571558K.SUZUKIhighreactivity:theligandexchangegeneratesahafnoceneperchloratecomplexwhich,asahighlyelectrophilic14electronspecies,
