4.Electrophilic Additions to Carbon-Carbon Multiple Bonds 英文学习材料

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1、4ElectrophilicAdditionstoCarbon-CarbonMultipleBondsIntroductionAdditionofelectrophilicreagentsisoneofthemostgeneralandusefulreactionsofalkenesandalkynes.Thischapterfocusesonreactionsthatproceedthroughpolarintermediatesortransitionstructures.Wediscussthefundamentalmechanist

2、iccharacteristicsofthisclassofreactionsinChapter5ofPartA,includingproton-catalyzedadditionsofwaterandalcoholsandtheadditionofhydrogenhalides.Otherelectrophilicreagentsthatweconsidertherearethehalogensandpositivehalogencompounds,electrophilicsulfurandseleniumreagents,andmer

3、curicsalts.Hydrobo-rationisanotherimportanttypeofelectrophilicadditiontoalkenes.Inthepresentchapter,weemphasizesyntheticapplicationofthesereactions.Forthemostpart,electrophilicadditionsareusedtointroducefunctionalityatdoubleandtriplebonds.Whenthenucleophileadditionstepisin

4、tramolecular,anewheterocyclicringisformed,andthisisaveryusefulsyntheticmethod.E+E+E(C)nE(C)or(C)(C)nnnNuNuNu:Nu:exo–cyclizationendo–cyclizationCarbonylcompoundscanreactwithelectrophilesviatheirenolisomersorequivalents,andthesereactionsresultin-substitution.OOHδ+δ−OXYR′CH2

5、RR′CHRR′CHRX289290Severalothertypesofadditionreactionsofalkenesarealsoofimportanceandthesearediscussedelsewhere.NucleophilicadditionstoelectrophilicalkenesarecoveredCHAPTER4inSection2.6andcycloadditionsinvolvingconcertedmechanismsareencounteredinElectrophilicAdditionsSecti

6、ons6.1to6.3.FreeradicaladditionreactionareconsideredinChapter11.toCarbon-CarbonMultipleBonds4.1.ElectrophilicAdditiontoAlkenes4.1.1.AdditionofHydrogenHalidesHydrogenchlorideandhydrogenbromidereactwithalkenestogiveadditionproducts.Inearlywork,itwasobservedthatadditionusuall

7、ytakesplacetogivetheproductwiththehalogenatomattachedtothemore-substitutedcarbonofthedoublebond.ThisbehaviorissufficientlygeneralthatthenameMarkovnikov’srulewasgiventothestatementdescribingthismodeofaddition.Thetermregioselectiveisusedtodescribeadditionreactionsthatproceed

8、selectivelyinonedirectionwithunsymmetricalalkenes.1Arudimentarypictureofthereactionmechan