微波辅助以水作溶剂的合成.docx
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微波辅助以水作溶剂的合成.docx
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微波辅助以水作溶剂的合成
Chem.Rev.2007,107,2563-2591
2563
Microwave-AssistedSynthesisinWaterasSolvent
DorisDallingerandC.OliverKappe*
ChristianDopplerLaboratoryforMicrowaveChemistry(CDLMC)andInstituteofChemistry,Karl-Franzens-UniversityGraz,Heinrichstrasse28,A-8010Graz,Austria
ReceivedJuly26,2006
Contents
1.Introduction2563
2.OrganicSynthesisinWater2564
3.Microwave-AssistedOrganicSynthesis2565
4.MicrowaveChemistryinWatersGeneralAspects2566
5.Transition-Metal-CatalyzedReactions2567
5.1.SuzukiReactions2567
5.2.HeckReactions2572
5.3.SonogashiraReactions2573
5.4.StilleReactions2574
5.5.HiyamaReactions2574
5.6.CarbonylationReactions2574
5.7.CyanationReactions2575
6.OtherTransition-Metal-MediatedReactions2575
7.N-,O-,S-Functionalizations2576
withmanynewtechnologiesbeingdevelopedeachyear.Intoday’sworld,syntheticchemistsinbothacademiaandindustryareconstantlychallengedtoconsidermoreenvi-ronmentallybenignmethodsforgenerationofthedesiredtargetmolecules.Amongthe12principlesofgreenchem-istry,3thedesireforutilizing“safersolvents”andto“designforenergyefficiency”canbeconsideredtwokeyprinciplesofrelevancetosyntheticchemists.
7.1.
N-Acylations
2576
thesis.4
7.2.
N-Alkylations
2576
solvent-
7.3.
N-Arylations
2577
liquids,
7.4.
O-andS-Functionalizations
2577
water.9,1
Solventusageisoftenanintegralpartofachemicalormanufacturingprocess.Theunavoidablechoiceofaspecificsolventforadesiredchemicalreactioncanhaveprofoundeconomical,environmental,andsocietalimplications.Thepressingneedtodevelopalternativesolventstosomeextentoriginatesfromtheseimplicationsandconstitutesanessentialstrategyundertheemergingfieldofgreenchemistry.1-3Towardthisend,considerableeffortshavebeendevotedtodevelopandusenontraditionalsolventsforchemicalsyn-Suchunconventionalmediainclude,amongothers,
freeconditions,5supercriticalcarbondioxide,6ionic
7perfluorinatedsolvents,8andlastbutnotleast
8.HeterocycleSynthesis2578
8.1.Five-MemberedN-Heterocycles2578
8.2.Six-MemberedO-Heterocycles2579
8.3.Six-MemberedN-Heterocycles2579
8.4.Six-MemberedN,S-Heterocycles2580
9.Mannich-TypeMulticomponentReactions2581
10.NucleophilicSubstitutions2581
10.1.NucleophilicAromaticSubstitutions2581
11.EpoxideRing-OpeningReactions2582
12.Diels-AlderCycloadditions2583
13.DecarboxylationsandHydrolyses2583
14.Protection/DeprotectionReactions2585
15.MiscellaneousReactions2585
16.ReactionsinNear-CriticalWater2587
17.FutureProspectsandChallenges2588
18.Acknowledgments2588
19.References2589
1.Introduction
Withinthepastdecade,greenchemistryhasattainedthestatusofamajorscientificdiscipline.1,2Theinvestigationandapplicationofgreenchemistryprincipleshasledtothedevelopmentofcleanerandmorebenignchemicalprocesses,
*Towhomthecorrespondenceshouldbeaddressed.Phone:
+43-316-380-5352.Fax:
+43-316-380-9840.E-mail:
oliver.kappe@uni-graz.at.
0Thereiswidespreadcurrentdebateovertherelative“greenness”oftheseindividualreactionmedia,butwatercanundoubtedlybeconsideredthecleanestsolventavailable,andtheuseandreleaseofcleanwaterclearlywillhavetheleastimpacttotheenvironment.11
Ontheotherhand,formanychemicalprocessesamajoradverseeffecttotheenvironmentistheconsumptionofenergyforheatingandcooling.Toovercometheseproblemsitishighlydesirabletodevelopefficientmethodsthatusealternativeenergysourcessuchasultrasoundormicrowaveirradiationtofacilitatechemicalreactions.Inparticular,theuseofmicrowaveenergytodirectlyheatchemicalreactionshasbecomeanincreasinglypopulartechniqueinthescientificcommunity.12-14Althoughthereisstillconsiderabledebateandspeculationonthenatureand/orexistenceofso-called“nonthermal”microwaveeffectsthatcouldprovidearatio-nalizationfortheoftenobservedsignificantrateandyieldenhancements,14thereislittledoubtthatmicrowaveheatingwillbecomeastandardtechniqueinmostlaboratorieswithinafewyears.Ismicrowavechemistrygreenchemistry?
Arecentstudycomparingtheenergyefficiencyofconventionaloil-bathsynthesis(heatingbyconductionandconvectioncurrents)andmicrowave-assistedsynthesis(direct“molec-ular”heatingofthereactionmixture)hasindicatedthatformostchemicaltransformationsasignificantenergysavings(upto85-fold)canbeexpectedusingmicrowavesasanenergysourceonalaboratoryscale.15Ifthosedataalsoholdtrueforlargerscalemicrowaveapplicationsonapilotorproductionscaleremainstobeseen.16Thepossibilityofperformingreactionsinaveryshorttimeperiodbydirect
10.1021/cr0509410CCC:
$65.00©2007AmericanChemicalSocietyPublishedonWeb04/24/2007
DorisDallingerwasborninSalzburgin1976andstudiedchemistryattheUniversityofGraz,Austria.In2001sheobtainedherdiplomadegreeinthefieldofsolid-phaseorganicsynthesis.ShecontinuedwithPh.D.workinthegroupofProfessorC.OliverKappeonprojectsrelatedtomicrowavechemistryandhigh-throughputsynthesis.AfterreceivingherPh.D.degreein2005,shejoinedtheChristianDopplerLaboratoryforMicrowaveChemistryattheUniversityofGrazin2006asapostdoctoralresearchassociateandiscurrentlyengagedinprojectsrelatedtospecificmicrowaveeffectsandthescale-upofmicrowave-assistedreactions.
C.OliverKappeisAssociateProfessorofOrganicChemistryandDirectoroftheChristianDopplerLaboratoryforMicrowaveChemistry(CDLMC)attheUniversityofGraz,Austria.Hereceivedhisdiploma(1989)andhisdoctoral(1992)degreesinOrganicChemistryfromtheUniversityofGraz,whereheworkedwithProfessorGertKollenzoncycloadditionandrearrangementreactionsofacylketenes.AfterperiodsofpostdoctoralresearchworkonreactiveintermediatesandmatrixisolationspectroscopywithProfessorCurtWentrupattheUniversityofQueenslandinBrisbane,Australia(1993-1994),andonsyntheticmethodology/alkaloidsynthesiswithProfessorAlbertPadwaatEmoryUniversityinAtlanta,GA(1994-1996),hemovedbacktotheUniversityofGrazin1996tostarthisindependentacademiccareer.Heobtainedhis“Habilitation”in1998inOrganicChemistry,andsince1999hehasheldthetenuredpositionofanAssociateProfessorofChemistryattheUniversityofGraz.In2003hespentasabbaticalattheScrippsResearchInstitute(LaJolla,CA)inthegroupofProfessorK.BarrySharpless.
interactionofmicrowaveenergywiththereactionmixtureasopposedtotheindirecttransferofenergybyutilizinganoilbathorsimilardevicecertainlycanbeconsidered“green”,notonlybecauseofthereducedenergyconsumption,butalsobecauseoftheassociatedtimesavings,therebyincreas-ingefficiency.
Duringthepasttwodecadesmanypublicationshavedescribedthesuccessfulcombinationofmicrowaveirradia-tionasanonclassicalenergysourcewithalternativereactionmedia.Particularlynoteworthyistheconceptofperformingmicrowavesynthesisundersolvent-free(drymedia)condi-tions,wherethereagentsarereactedneatorpreadsorbed
ontoeitheramoreorlessmicrowavetransparent(silica,alumina,orclay)orstronglyabsorbing(graphite)inorganicsupportthatadditionallycanbedopedwithacatalystorreagent.17Particularlyintheearlydaysofmicrowavesynthesisthesolvent-freeapproachwasverypopularsinceitallowedthesafeuseofdomestichouseholdmicrowaveovensandstandardopen-vesseltechnology.Morerecentlymicrowave-assistedreactionsusingionicliquidsassolventshavebeendescribed.18Ionicliquidsinteractveryefficientlywithmicrowavesthroughanionicconductionmechanismandarerapidlyheatedatrateseasilyexceeding10︒C/swithoutanysignificantpressurebuildup.Therefore,safetyproblemsarisingfromoverpressurizationofheatedsealedreactionvesselscanbeminimized.Similarly,microwavechemistryhasbeenconductedinconjunctionwiththeuseoffluoroussolventsorfluorousreagents/catalysts.19Theadvantageofmicrowaveheatingliesintherapidcoalescenceoftheorganicandfluorousphasetoformahomogeneoussolution.
Asfaraswaterassolventisconcerned,numerousrecentpublicationsreportthecombinationofwaterasanenviron-mentallybenignsolventforchemicaltransformationswiththeuseofmicrowaveirradiationasanefficientheatingmethod.EarlyworkinthisareawasconductedbyStraussinthemid-1990sandinvolvedthegenerationofsuperheatedwaterusingadedicatedreactorformicrowaveheatingofsolventsundersealed-vesselconditions.20-22Inrecentyearsthecombinationofthesetwoprominentgreenchemistryprinciples,3“microwaves”and“water”,hasbecomeverypopularandreceivedsubstantialinterestduetotheworkofLeadbeater23andotherswhodemonstratedthatagreatvarietyofsyntheticorganictransformationssinparticular,transition-metal-catalyzedprocessesscanbecarriedoutveryefficientlyandrapidlyundertheseenvironmentallybenignconditions.Despitethisfactnogeneralandcomprehensiveliteraturesurveyonthistopicexists.
Thisreviewwillcovermicrowave-assistedorganicsyn-thesis(MAOS)usingwaterassolvent(orcosolvent)rangingfromambienttemperaturestochemistryperformedinnear-criticalwaterat300︒Cand80barpressure.Examplesfromtheliteraturewilldealmainlywithsyntheticorganicchemistryrangingbacktothelate1980swhenthefirstexamplesofmi
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