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Anef cientorganocatalyticmethodforconstructingbiarylsthrougharomaticC–Hactivation
Chang-LiangSun1,HuLi1,Da-GangYu1,MiaoYu1,XiaoZhou1,Xing-YuLu1,KunHuang1,Shu-FangZheng2,Bi-JieLi1andZhang-JieShi1*
ThedirectfunctionalizationofC–Hbondshasdrawntheattentionofchemistsforalmostacentury.C–Hactivationhasmainlybeenachievedthroughfourmetal-mediatedpathways:oxidativeaddition,electrophilicsubstitution,s-bondmetathesisandmetal-associatedcarbene/nitrene/oxoinsertion.However,theidenti cationofmethodsthatdonotrequiretransition-metalcatalystsisimportantbecausemethodsinvolvingsuchcatalystsareoftenexpensive.Anotheradvantagewouldbethattherequirementtoremovemetallicimpuritiesfromproductscouldbeavoided,animportantissueinthesynthesisofpharmaceuticalcompounds.Here,wedescribetheidenti cationofacross-couplingbetweenaryliodides/bromidesandtheC–Hbondsofarenesthatismediatedsolelybythepresenceof1,10-phenanthrolineascatalystinthepresenceofKOt-Buasabase.Thisapparentlytransition-metal-freeprocessprovidesanewstrategywithwhichtoachievedirectC–Hfunctionalization.
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irectC–Hbondtransformationisafundamentallyimportantsubjectinorganicsynthesisinbothacademicandindustrialprocesses.Thepursuitofef cientmethodstodirectlytrans-formC–Hbondstootherfunctionalgroupsdatesbacktoearlyinthetwentiethcentury1–5.SelectivefunctionalizationofaromaticC–Hbondsisnowanimportantaspectofthisrathergeneral eldduetotheuniversalexistenceofaromaticfunctionalitiesinnatureandthesyntheticworld.‘Fenton’chemistry6–9andFriedel–Craftsreactions10,11areearlyexamplesoftransformationsofarylC–http://www.77cn.com.cnter,variouscatalyticsystemsweredeveloped.Reactionsrelyingonlatetransitionmetalcatalystshave ourishedinparticular12–19.Thesetransition-metal-catalysedprocessescanbesummarizedintofourgeneralmechanisms(Fig.1):(a)Friedel–Crafts-typeelectrophilicattackbyhigh-valenttransition-metalspecies,followedbydeprotonation12,16–18,20–23;(b)oxidativeadditionofC–Hbondstolow-valentelectron-richtran-sition-metalcatalysts24–28;(c)s-bondmetathesis19;and(d)metal-associatedcarbene/nitrene/oxoinsertion13–15,29.
Ourresearchhasfocusedonthecatalyticcross-couplingreac-tionsofarenestoconstructbiaryls30.Inparticular,weareinterestedinthecross-couplingofaromaticC–Hbondswithfunctionalizedarenesinanatom-economicandwaste-freemanner.Suchreactionshavebeendeemedtobeamongthemost‘aspirational’reactionsasyetunderdevelopedinthe‘keygreenchemistryresearchareas’favouredbythepharmaceuticalindustry.Theresultingbiarylscaf-foldsareprivilegedstructuralunitsthathavediverseapplicationsinthe eldsofpharmaceuticals,fragrances,dyesandagrochemicals.Inthepastfewdecades,manymethodshavebeendevelopedtodirectlyfunctionalizeC–Hbonds,ofteninvolvingthelatetransitionmetalsornoblemetals31–44.Theneedforhighcatalystloadinginsomeoftheseprocessesresultsinahigheconomiccost.Thepres-enceofheavytransition-metalimpuritiesinthe nalproductsalsopresentsamajorproblemregardingpuri cation,further
increasingthecostsinvolved.Thedevelopmentofef cientandtransition-metal-freeprocesseswillsigni cantlychangesyntheticstrategiesfortheassemblyofbiarylstructures.Herein,wediscuss
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Figure1|DirectaromaticC–Htransformations.a,C–Hfunctionalizationthroughelectrophilicattackbyhigh-valenttransitionmetals.M¼Pt(II),
Pt(IV),Pd(II),Pd(IV),Au(III),Cu(III),andsoon.b,OxidativeadditionofC–Htolow-valenttransition-metalcomplexestocarryoutC–Hfunctionalization.M¼Ir(I),Rh(I),Ru(0),andsoon.c,DirectC–Htransformationvias-bondmetathesis.M¼Ir(III),Zr(IV),andsoon.d,DirectaromaticC–Htransformationviacarbeneinsertion.Ineachofa–dtheformed
organometallicintermediatecangoontoformanewC–Cbond.e,Inthisreport,cross-couplingofareneswitharyliodides/bromidesintheabsenceoftransition
metals.M¼transitionmetal,Ar¼aryl,X¼IorBr.
BeijingNationalLaboratoryofMolecularSciences(BNLMS)andKeyLaboratoryofBioorganicChemistryandMolecularEngineeringofMinistryofEducation,CollegeofChemistryandMolecularEngineering,PekingUniversity,Beijing100871,China,2DepartmentofChemistryandMaterialsScience,SichuanNormalUniversity,Chengdu,Sichuan610068,China.*e-mail:zshi@http://www.77cn.com.cn
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