配体 双恶唑啉

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1、Inchemistry,bis(oxazoline)ligands双恶唑啉配体(oftenabbreviatedBOXligands)areaclassofprivileged特许的，专用的chiralligandscontainingtwooxazolinerings.TheyaretypicallyC2symmetric对称andexistinawidevarietyofforms;withstructuresbasedaroundCH2orpyridinelinkersbeingparticularlycommon(oftengeneralised概括，归纳BOXandPyBOX

2、respectively).Thecoordinationcomplexesofbis(oxazoline)ligandsareusedextensivelyinasymmetriccatalysis.SynthesisFurtherinformation:SynthesisofoxazolineringsThesynthesisofoxazolineringsiswellestablishedandingeneralproceededviathecyclisationofa2aminoalcoholwithanyofanumberofsuitablefunctionalgroups.

3、Inthecaseofbis(oxazoline)s,synthesisismostconvenientlyachievedbyusingbi-functionalstartingmaterials;asthisallowsbothringstobeproducedatonce.Ofthematerialssuitable,dicarboxylicordinitrilecompoundsarethemostcommonlyavailableandhencethemajority多数bis(oxazoline)ligandsareproducedfromthesematerials.Par

4、tofthesuccessoftheBOXandPyBOXmotifs动机;基本图案liesin在于;位于theirconvenientonestepsynthesisfrommalononitrile丙二氰anddipicolinicacid,whicharecommerciallyavailableatlowexpense.Chiralityisintroducedwiththeaminoalcohols,asthesearepreparedfromaminoacidsandhencearechiral(e.g.valinol).TheadvantagesC2-symmetryThe

5、lefthandstructurehasaC2rotationalaxisæksɪs轴whereastherighthandstructureisasymmetric.Arrows箭状物;箭头记号indicatethetheoreticalattacktrajectories轨道ofreagents,identical同一的coloursleadtoidenticaltransitionstates(andhenceproducts)withredarrowsbeingdisfavouredduetostericrepulsion空间排斥.Inbis(oxazoline)complex

6、esthemetalisheldclosetothestereogeniccentres立体异构中心,whichwillstronglyinfluencetheenantioselectivityofanyprocesstakingplacethere.HowevertheC2symmetryoftheligandisalsoimportantincontrollingthisenatioselectivity.Whilethepresenceofanysymmetryelementwithinaligandintended意欲，计划forasymmetricinductionmigh

7、tappearcounterintuitive违反直觉的,asymmetricinduction不对称诱导onlyrequiresthattheligandbechiral(i.e.即，换言之havenoimproperrotationaxis);itdoesnothavetobeasymmetric(i.e.devoidof缺乏的anysymmetryelement).C2symmetryactuallyimprovesthee