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Reactions of epoxides involve attack by aReactions of epoxides involve attack by anucleophile and proceed with ring-opening.nucleophile and proceed with ring-opening.For ethylene oxide:For ethylene oxide:
Nu—H Nu—H ++
Nu—Nu—CHCH22CHCH22O—O—HH
HH22CC CHCH22
OO
In general...In general...
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For epoxides where the two carbons of theFor epoxides where the two carbons of thering are differently substituted:ring are differently substituted:
In general...In general...
CHCH22
OO
CC
RR
HH
Nucleophiles attack hereNucleophiles attack herewhen the reaction iswhen the reaction iscatalyzed by acids:catalyzed by acids:
Anionic nucleophilesAnionic nucleophilesattack here:attack here:
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Nucleophilic Ring-OpeningNucleophilic Ring-Opening
Reactions of EpoxidesReactions of Epoxides
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NaOCHNaOCH22CHCH33
CHCH33CHCH22OHOH
(50%)(50%)
ExampleExample
OO
HH22CC CHCH22
CHCH33CHCH22OO CHCH22CHCH22OOHH
![Page 5: Reactions of epoxides involve attack by a nucleophile and proceed with ring-opening. For ethylene oxide: Nu—H + Nu—CH 2 CH 2 O—H H2CH2CH2CH2C CH 2 O In](https://reader035.vdocuments.mx/reader035/viewer/2022062500/5697bf821a28abf838c858ee/html5/thumbnails/5.jpg)
••••••••OO
HH22CC CHCH22
CHCH33CHCH22 OO••••
•••• ••••––
MechanismMechanism
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••••••••OO
HH22CC CHCH22
CHCH33CHCH22 OO••••
•••• ••••––
––••
••CHCH33CHCH22 OO
••••
•••• ••••CHCH22CHCH22 OO••••
MechanismMechanism
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••••••••OO
HH22CC CHCH22
CHCH33CHCH22 OO••••
•••• ••••––
––••
••CHCH33CHCH22 OO
••••
•••• ••••CHCH22CHCH22 OO••••
OO CHCH22CHCH33••••
••
••
––
HH
MechanismMechanism
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••••••••OO
HH22CC CHCH22
CHCH33CHCH22 OO••••
•••• ••••––
––••
••CHCH33CHCH22 OO
••••
•••• ••••CHCH22CHCH22 OO••••
••
••CHCH33CHCH22 OO
••••
••••CHCH22CHCH22 OO
••••HH OO CHCH22CHCH33
••••••
••••
••
––
OO CHCH22CHCH33••••
••
••
––
HH
MechanismMechanism
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(99%)(99%)
ExampleExample
OO
HH22CC CHCH22
KSCHKSCH22CHCH22CHCH22CHCH33
ethanol-water, 0°Cethanol-water, 0°C
CHCH22CHCH22OOHHCHCH33CHCH22CHCH22CHCH22SS
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StereochemistryStereochemistry
Inversion of configuration at carbon being Inversion of configuration at carbon being attacked by nucleophileattacked by nucleophile
Suggests SSuggests SNN2-like transition state2-like transition state
NaOCHNaOCH22CHCH33
CHCH33CHCH22OHOHOO
HH
HH HH
OOHH
HH
OCHOCH22CHCH33
(67%)(67%)
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NHNH33
HH22OO
(70%)(70%)
RR
SS
RR
RR
StereochemistryStereochemistry
HH33CC CHCH33
HH33CC CHCH33
OOHH
HHHH
HH OHOHHH22NN
Inversion of configuration at carbon being Inversion of configuration at carbon being attacked by nucleophileattacked by nucleophile
Suggests SSuggests SNN2-like transition state2-like transition state
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NHNH33
HH22OO
(70%)(70%)
++ --
RR
SS
RR
RR
StereochemistryStereochemistry
HH33CC CHCH33
HH33CC CHCH33
OOHH
HHHH
HH OHOHHH22NN
HH33NN OO
HH33CCHH
HH33CCHH
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NaNaOCHOCH33
CHCH33OHOHCHCH33CCHH CCHCCH33
CHCH33
OOHH
CHCH33OO
(53%)(53%)
CCCC
HH
HH33CC CHCH33
CHCH33OO
consistent with Sconsistent with SNN2-like transition state2-like transition state
Anionic nucleophile attacks less-crowded carbonAnionic nucleophile attacks less-crowded carbon
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(90%)(90%)
Hydride attacksHydride attacksless-crowdedless-crowded
carboncarbon
Lithium aluminum hydride reduces epoxidesLithium aluminum hydride reduces epoxides
OO
HH22CC CH(CHCH(CH22))77CHCH33
1. LiAlH1. LiAlH44, diethyl ether, diethyl ether
2. H2. H22OO
OOHH
HH33CC CH(CHCH(CH22))77CHCH33
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Acid-Catalyzed Ring-OpeningReactions of Epoxides
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ExampleExample
OO
HH22CC CHCH22CHCH33CHCH22OOCHCH22CHCH22OOHH
(87-92%)(87-92%)
CHCH33CHCH22OCHOCH22CHCH22OCHOCH22CHCH33 formed only on heating formed only on heating
and/or longer reaction times and/or longer reaction times
CHCH33CHCH22OHOH
HH22SOSO44, 25°C, 25°C
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ExampleExample
OO
HH22CC CHCH22 HBrHBr
10°C10°CBrBrCHCH22CHCH22OOHH
(87-92%)(87-92%)
BrCHBrCH22CHCH22Br formed only on heating and/or Br formed only on heating and/or
longer reaction timeslonger reaction times
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MechanismMechanism
••••OO
HH22CC CHCH22++
HHBrBr••••
••••••••
––••••
••••OO
HH22CC CHCH22++
••••HHBrBr
••••••••
••••
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MechanismMechanism ••••OO
HH22CC CHCH22++
HH
••••
••
••OO••••
BrBr
CHCH22CHCH22 HH
••••••••
BrBr••••
••••••••
––••••
••••OO
HH22CC CHCH22++
••••HHBrBr
••••••••
••••
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Acid-Catalyzed Hydrolysis of Ethylene OxideAcid-Catalyzed Hydrolysis of Ethylene Oxide
••••OO
HH22CC CHCH22++
HH
••••OO
HH22CC CHCH22++
••••
OO••••
HH
HH
HH++ OO••••
HH
HH
••••
Step 1Step 1Step 1Step 1
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Acid-Catalyzed Hydrolysis of Ethylene OxideAcid-Catalyzed Hydrolysis of Ethylene Oxide
••••OO
HH22CC CHCH22
OO••••
••••
++
HHHH
HH
Step 2Step 2Step 2Step 2
••••++
••
••OO
OO
CHCH22CHCH22
HH
HH
HH
••
••
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Acid-Catalyzed Hydrolysis of Ethylene OxideAcid-Catalyzed Hydrolysis of Ethylene Oxide
OO••••
••••
HH
HH
Step 3Step 3Step 3Step 3
••••++
••
••OO
OO
CHCH22CHCH22
HH
HH
HH
OO ••••
HH
HH++
HH
••••
••
••OO
OO
CHCH22CHCH22
HH
HH
••••
••
••
••
••
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Acid-Catalyzed Ring Opening of EpoxidesAcid-Catalyzed Ring Opening of Epoxides
nucleophile attacks more substituted carbon nucleophile attacks more substituted carbon of protonated epoxideof protonated epoxide
inversion of configuration at site of nucleophilic inversion of configuration at site of nucleophilic attackattack
Characteristics:Characteristics:
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CHCH33OHOHCHCH33CHCH CCCHCH33
CHCH33OOHH
OCHOCH33
(76%)(76%)
CCCC
HH
HH33CC CHCH33
CHCH33OO
consistent with carbocation character at consistent with carbocation character at transition statetransition state
Nucleophile attacks more-substituted carbonNucleophile attacks more-substituted carbon
HH22SOSO44
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StereochemistryStereochemistry
Inversion of configuration at carbon being Inversion of configuration at carbon being attacked by nucleophileattacked by nucleophile
(73%)(73%)
HH
HH
OO HBrHBr
HHOOHH
BrBrHH
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(57%)(57%)
RR
SS
RR
RR
StereochemistryStereochemistry
HH33CC CHCH33
HH33CC CHCH33
OOHH
HHHH
HH OHOHCHCH33OO
Inversion of configuration at carbon being Inversion of configuration at carbon being attacked by nucleophileattacked by nucleophile
CHCH33OHOH
HH22SOSO44
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RR
SS
RR
RR
StereochemistryStereochemistry
HH33CC CHCH33
HH33CC CHCH33
OOHH
HHHH
HH OHOHCHCH33OOCHCH33OHOH
HH22SOSO44
++ ++CHCH33OO OO
HH33CCHH
HH33CCHH
HH++
HH