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1、www.elsevier.nllocatejganchemJournalofganometallicChemistry609(2000)137–151MethodsofenhancementofreactivityivityofsodiumbohydridefapplicationsinganicsynthesisMariappanPeriasamyMuniappanThirumalaikumarSchoolofChemistryUni

2、?ersityofHyderabadCentralUni?ersityPOHyderabad500046IndiaReceived29February2000receivedinrevisedfm16April2000AbstractNaBH4doesnotreducecarboxylicacidsestersaesnitrilesunderambientconditions.HoweverthereactivityofNaBH4can

3、beenhancedbytheadditionofcertainadditives.FexampleadditionofiodinetoNaBH4inTHFprovidesH3B–THFthatisusefulfhydrobationsreductionsofvariousfunctionalgroups.ThealdehydesketonesarereducedinafastmannerbytheNaBH4reagent.Evenso

4、theivitiesrealisedinsuchreductionscanbeenhancedusingNaBH4alongwithanotheradditive.InthisarticlevariousmethodsusedftheenhancementofreactivityivityofNaBH4inganicsynthesisaredescribed.?2000ElsevierScienceS.A.Allrightsreserv

5、ed.Keywds:SodiumbohydrideEnhancementofreactivityAdditivesReductionofganics1.IntroductionMetalhydridesarevaluablereagentsinmodernganicchemistry.ThemostfrequentlyusedhydrideistheNaBH4reagent.Itisamildinexpensiveinvaluabler

6、eagentfapplicationsinawiderangeofreductionprocesses.Itisthereagentofchoicefthereductionofaldehydesketonestoalcohols[1]imines[2]iminiumsalts[3]toamineswithproticsolvents[4].Thecarboxylicacidsestersaesnitrilesaremeresistan

7、ttowardsNaBH4[1].HoweverthereactivityofNaBH4canbeenhancedbycarryingoutthereactioninthepresenceofcertainadditives.InthisarticlevariousmethodsofenhancementofreactivityivityofNaBH4usingadditivesfapplicationsinganicsynthesis

8、aredescribed.2.HydrobationofalkenesalkynesHydrobationofcarbon?carbonmultiplebondsprovidesamethodfthesynthesisofthevaluableganobaneintermediateswithhighregiostereospecificities[5].HisticallyBrownSubbaRaodiscoveredthehydro

9、bationreactionduringtheirinvestigationoftheactivationofNaBH4fthereductionofestersusingAlCl3[6].TheuseofBF3intheplaceofAlCl3ledtomeeffectiveutilisationofthehydridefthegenerationofdibaneB2H6boraneLewisbasecomplexes(Eqs.1–3

10、)[7].9RCH?CH2AlCl3?????diglyme3(RCH2CH2)3BAlH33NaCl(1)12RCH?CH23NaBH44BF3?????diglyme4(RCH2CH2)3B3NaBF4(2)(RCH2CH2)3B3H2O2NaOH?3RCH2CH2OHNaB(OH)4(3)Althoughseveralofthesebanecomplexesarecommerciallyavailable(e.g.H3B–THFH

11、3B–SMe2H3B–NR3)therehavebeensustainedefftstowardsthedevelopmentofalternativesimpleconvenientmethodsofgenerationofbanesinsitufhydroboration.In1963itwasreptedthata1:1mixtureofNaBH4CH3COOHhydrobatesalkenes[8a].Lateramodifie

12、dprocedurefhydrobanesusingNaBH4–CH3COOHwasrepted(Eq.(4))[8b].Crespondingauth.Tel.:91403010904fax:91403010120.Emailaddress:(M.Periasamy)0022328X00$seefrontmatter?2000ElsevierScienceS.A.Allrightsreserved.PII:S0022328X(00)0

13、02102M.PeriasamyM.ThirumalaikumarJournalofganometallicChemistry609(2000)137–151139VeryrecentlyithasbeenreptedthatthetetrabutylammoniumbohydrideliberatesdibaneinsolventssuchasCH2Cl2CHCl3CCl4.Anumberofterminalinternalcycli

14、calkeneswerehydrobatedusingthisbohydride(Eq.(16))[25].(16)The1alkynesundergodihydrobationtoyieldthecrespondingterminalalcoholsafteroxidation.Generallythedisubstitutedalkynesgivevinylbanesthatonoxidationoffdketonesasthema

15、jproduct(Eqs.(17)(18))[2526].Howeverthediphenylacetyleneyields12diphenylethanolasthemajproductthroughdihydrobationundertheseconditions.C6H5C?CC6H5??????????????NaBH4?Bu4NCl?CHCl3C6H5CH(OH)CH2C6H583%(17)CH3CH2C?CCH2CH3???

16、???????????NaBH4?Bu4NCl?CHCl3CH3CH2CO(CH2)2CH390%(18)ThePdCl2–NaBH4–polyethyleneglycol(PEG)–CH2Cl2systemiseffectivefhydrogenationofcarbon?carbontriplebondstothecrespondingcisalkenes(Eq.(19))[27].Thisreagenthasadvantageso

17、ffasterrateshigherivity.(19)3.ReductionofcarboxylicacidsTheNaBH4givesacyloxybohydridespeciesonreactionwithcarboxylicacidsinTHFthathydrobateolefins.Theacyloxymoietiesinsuchacyloxybohydridesremainunchangedunderambientcondi

18、tions.Howeveronehalfoftheacyloxymoietyundergoesreductionuponheatingtogivethecrespondingalcohol(Eq.(20))[28].(20)AsimilarreactionwasalsoobservedusingNaBH4RCOOHcatecholat25C(Eq.(21))[29].(21)Aliphaticcarboxylicacidsareredu

19、cedbyNaBH4tothecrespondingalcoholsingoodyieldswhenRCOOHCF3COOHareusedin1:1ratiounderambientconditions(Eq.(22)).Howeverthearomaticacidsgivepoyields(e.g.benzoicacid20%).AlsotheNaBH4–CF3COOHcombinationisgoodfthereductionofa

20、liphaticcarboxylicacids(65–95%yields).Againaromaticacidsgiveporesultsundertheseconditions(30%).(22)TheZnCl2–NaBH4reagentsystemreadilyreducesbothaliphaticaromaticacidstothecrespondingalcoholsinrefluxingTHF(Eq.(23))[30].Th

21、ereactionrequiresonlystoichiometricquantitiesofhydridefthisconversion.Alsodicarboxylicacidsarereducedtothecrespondingdiolsundertheseconditions.RCOOH??????????NaBH4?ZnCl2THF?RCH2OHR=alkylaryl70?95%(23)Thereagentpreparedus

22、ingZrCl4NaBH4reducesthecarboxylicacidsinexcellentyieldsundermildconditions(Eq.(24))[31].PhCOOH??????????NaBH4?ZrCl4THFrt5hPhCH2OH85%(24)CarboxylicacidsarereducedtothecrespondingalcoholsunderambientconditionsbytheNaBH4–I2

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