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1、5ReductionofCarbon-CarbonMultipleBonds,CarbonylGroups,andOtherFunctionalGroupsIntroductionThesubjectofthischapterisreductionreactionsthatareespeciallyimportantinsynthesis.Reductioncanbeaccomplishedbyseveralbroadmethodsincludingadditionofhydrogenand/orelectronstoamoleculeorbyremovalo
2、foxygenorotherelectroneg-ativesubstituents.Themostwidelyusedreducingagentsfromasyntheticpointofviewaremolecularhydrogenandhydridederivativesofboronandaluminum,andthesereactionsarediscussedinSections5.1through5.3.Asmallergroupofreactionstransfershydridefromsiliconorcarbon,andtheseare
3、thetopicofSection5.4.Certainreductionsinvolvingafreeradicalmechanismusesilanesorstannanesashydrogenatomdonors,andthesereactionsareconsideredinSection5.5.Otherimportantproce-duresusemetalssuchaslithium,sodium,orzincaselectrondonors.Reductionbymetalscanbeappliedtocarbonylcompoundsanda
4、romaticringsandcanalsoremovecertainfunctionalgroups.AdditionofHydrogenH2[MH–]42M·R2CXR2CHXHR2CXR2CHXHR2CX+R2CHXH2HcatalytichydrogenationhydridereductionreductionbymetalsX=CR′2,O,NR′X=O,NR′X=O,NR′367368ReductiveRemovalofFunctionalGroupsCHAPTER52M·R′3ZHR3CY+R3CH+HYRCYRCH+R′ZYReduction
5、of2H333Carbon-CarbonMultipledissolvingmetalshydrogenatomdonorsBonds,CarbonylGroups,andOtherY=halogen,oxygensubstituents,Y=halogen,thioesterFunctionalGroupsα−tocarbonylgroupsZ=Sn,SiTherearealsoproceduresthatformcarbon-carbonbonds.Mostofthesereactionsbeginwithanelectrontransferthatgen
6、eratesaradicalintermediate,whichthenundergoesacouplingoradditionreaction.ThesereactionsarediscussedinSection5.6.X–XX–RCX+M·RC–·RCCR2orR2CCR2222XOM·=Na0,TiII,SmIIreductivecouplingReductiveremovalofoxygenfromfunctionalgroupssuchasketonesandaldehydes,alcohols,-oxyketones,anddiolsareal
7、soimportantinsynthesis.Thesereactions,whichprovideimportantmethodsforinterconversionoffunctionalgroups,areconsideredinSection5.7OHOOHORCH2RRRCHCHRR2CCR2R2CCR2RRRcarbonylmethylenecarbonylalkenediolalkenereductivedeoxygenation5.1.AdditionofHydrogenatCarbon-CarbonMultipleBondsThemostwi
8、delyusedmethodforad