环氧化物制备回顾与预览主要通过两种方法columbia有机化学课件13 html.pptx
16.9
PreparationofEpoxides:
AReviewandaPreview
Epoxidesarepreparedbytwomajormethods.
Bothbeginwithalkenes.reactionofalkeneswithperoxyacids
(Section6.18)conversionofalkenestovicinal
halohydrins,followedbytreatment
withbase(Section16.10)PreparationofEpoxides
16.10
ConversionofVicinalHalohydrins
toEpoxides
HOHBrHNaOHH2O(81%)HHOExample
OBrHH?
????
????
??
?–HOHBrHNaOHH2O(81%)HHOExamplevia:
anti
additionEpoxidationviaVicinalHalohydrinsBr2H2OOHBr
anti
additioninversionEpoxidationviaVicinalHalohydrinsBr2H2OOHNaOHcorrespondstooverallsynadditionof
oxygentothedoublebondBrO
anti
additioninversionEpoxidationviaVicinalHalohydrinsBr2H2OOHNaOHcorrespondstooverallsynadditionof
oxygentothedoublebondBrHH3CCH3OHHCH3H3CH
anti
additioninversionEpoxidationviaVicinalHalohydrinsBr2H2OOHNaOHcorrespondstooverallsynadditionof
oxygentothedoublebondBrHH3CCH3OHHH3CCH3HHCH3H3CH
16.11
ReactionsofEpoxides:
AReviewandaPreview
Allreactionsinvolvenucleophilicattack
atcarbonandleadtoopeningofthering. Anexampleisthereactionofethyleneoxide
withaGrignardreagent(discussedinSection15.4
asamethodforthesynthesisofalcohols).ReactionsofEpoxides
ReactionofGrignardReagents
withEpoxidesCH2CH2OMgXH3O+H2CCH2ORMgXRRCH2CH2OH
H2CCH2O+1.diethylether2.H3O+(71%)ExampleCH2MgClCH2CH2CH2OH
Reactionsofepoxidesinvolveattackbya
nucleophileandproceedwithring-opening.
Forethyleneoxide:Nu—H+Nu—CH2CH2O—HH2CCH2OIngeneral...
Forepoxideswherethetwocarbonsofthe
ringaredifferentlysubstituted:Ingeneral...CH2OCRH Nucleophilesattackhere
whenthereactionis
catalyzedbyacids: Anionicnucleophiles
attackhere:
16.12
NucleophilicRing-Opening
ReactionsofEpoxides
NaOCH2CH3CH3CH2OH(50%)ExampleOH2CCH2CH3CH2OCH2CH2OH
?
???OH2CCH2CH3CH2O?????
?–Mechanism
?
???OH2CCH2CH3CH2O?????
?––??CH3CH2O?????
?CH2CH2O??Mechanism
?
???OH2CCH2CH3CH2O?????
?––??CH3CH2O?????
?CH2CH2O??OCH2CH3?
???–