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ID:39255307
大小:3.68 MB
页数:77页
时间:2019-06-28
《4.Electrophilic Additions to Carbon-Carbon Multiple Bonds 英文学习材料》由会员上传分享,免费在线阅读,更多相关内容在学术论文-天天文库。
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
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