施老师的代表作
NATURECHEMISTRY
DOI:10.1038/NCHEM.862
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5
inthereactionreportedbyItamiandfacilitatethegenerationofaradicalspecies.Totestthissuggestion,weusedthemoretypicalradicalinitiatorazobisisobutyronitrile(AIBN)andtributyltinhydrideintheabsenceofKOt-Buandphenanthroline;thecross-couplingproductwasobserved,albeitinloweryield.Radicalquenchingstudiesalsosuggestthataradicalintermediateisimpor-tantinthetransformation.WhentetramethylpiperidineN-oxide(TEMPO,atypicalradicalscavenger)wasaddedunderthesameconditions,nodesiredproductwasobserved(forafulldescription,seeSupplementaryInformation).
Becauseunactivatedbenzeneshowedgoodreactivity,wefurtherproposethatboth1,10-phenanthrolineandapotassiumionmightinteractwiththearenesubstratethroughp,p-stacking50andion–pinteraction51topromotethereactivityofthebenzene(Fig.4).Onthebasisofthishypothesis,organiccompoundsthatarestructurallysimilartophenanthrolinesshowedgoodcatalyticreactivitytoactivatethearenes.Thismodelisconsistentwithourexperimentalresultsbasedonbothstericandelectronicfeatures.Ontheotherhand,otherinteractionsbetweenaKþionandtheC–Fof uoro-containingbenzenemightalsobefeasibleduetotheirhighreactivity.Furtherstudiestoextendthischemistryandcompletelyunderstandthistransformationareunderway.
Insummary,wereporthereanovelcross-couplingintheabsenceofanyaddedtransition-metalcatalyst.Thepresenceof1,10-phenanthrolineandexcessofKOt-Buareadequatetogivehighyieldsofcross-couplingbetweenaninertaromaticC–Handaryliodidesorbromides.Variousarylbromidesandiodidesshowedgoodreactivityinthistransformation.Extensiveexper-imentsindicatedthattheradicalwasinvolvedinthistransform-ation.Tothebestofourknowledge,suchreactivityhasnotbeenreportedpreviously.Itrepresentsaconceptualbreakthroughinper-formingcross-couplingbydirectC–Hfunctionalizationusinganorganocatalyst.
Methods
Generalexperimentalproceduresforcross-couplingofaryliodideswithbenzene.Aryliodides(0.2mmol,ifsolid)and1,10-phenanthroline(0.04mmol,20mol%)wereaddedtoSchlenktubes(driedbyaheatgun).KOt-Bu(0.4mmol,2.0equiv.)wasthenaddedinaglovebox.Benzene(2ml)andaryliodides(0.2mmol,ifliquid)wereaddedtothetubesusingasyringe.ThemixturewasthenstirredinasealedtubeunderaN2atmosphereat1008Cfor24h.Thereactionwasthencooledtoroomtemperature.Themixturewas lteredthroughashortplugofsilicagelandwashedwithcopiousquantitiesofethylacetate.Thecombinedorganicphasewasconcentratedundervacuum.Theproductwaspuri edthrough ashcolumnchromatographyon200–300-meshsilicagelwithpetroleumether/ethylacetateaseluent.
Generalexperimentalproceduresforcross-couplingofarylbromideswith
benzene.1,10-Phenanthroline(0.2mmol,40mol%)andarylbromides(0.5mmol,ifsolid)wereaddedtoSchlenktubes(driedbyaheatgun).KOt-Bu(1.5mmol,3.0equiv.)wasaddedtothetubesinaglovebox,thenbenzene(4ml)andarylbromides(0.5mmol,ifliquid)wereaddedusingasyringe.ThemixturewasstirredinasealedtubeunderaN2atmosphereat1008Cfor18h.Thereactionwasthencooledtoroomtemperature.Themixturewas lteredthroughashortplugofsilicagelandwashedwithcopiousquantitiesofethylacetate.Thecombinedorganicphasewasconcentratedundervacuum.Theproductwaspuri edusing ashcolumnchromatographyon200–300-meshsilicagelwithpetroleumether/ethylacetateaseluent.
Generalexperimentalproceduresforcross-couplingof4-iodoanisolewith
arenes.1,10-Phenanthroline(0.2mmol,40mol%)andarenes(40mmol,80equiv.,ifsolid)wereaddedintoSchlenktubes(driedbyaheatgun).KOt-Bu(1.5mmol,3.0equiv.)wasaddedinSchlenktubesinaglovebox.Arenes(4ml,ifliquid)and4-iodo/4-bromoanisole(0.5mmol)wereaddedintothetubesbysyringe.ThemixturewasstirredinasealedtubeunderaN2atmosphereat1208Cfor48h.Thereactionwascooledtoroomtemperature.Themixturewas lteredthroughashortplugofsilicagelandwashedwithcopiousethylacetate.Thecombinedorganicphasewasconcentratedundervacuum.Theproductwaspuri edthrough ashcolumnchromatographyon200–300-meshsilicagelwithpetroleumether/ethylacetateaseluent.
Received30April2010;accepted23August2010;publishedonline3October2010
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