Epoxidation of Alkenes
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Transcript of Epoxidation of Alkenes
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Epoxidation of Alkenes
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are examples of heterocyclic compounds
three-membered rings that contain oxygen
ethylene oxide propylene oxide
H2C CH2
O
H2C CHCH3
O
Epoxides
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Substitutive nomenclature: named as epoxy-substituted alkanes.
“epoxy” precedes name of alkane
1,2-epoxypropane 2-methyl-2,3-epoxybutane
H2C CHCH3
O
CHCH3
O
C
H3C
H3C
1
2 3 4
Epoxide Nomenclature
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cis-2-Methyl-7,8-epoxyoctadecane
Give the IUPAC name, including stereochemistry, for disparlure.
OH H
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peroxy acid
C C +
O
RCOOH
CC
O
+
O
RCOH
Epoxidation of Alkenes
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+ CH3COOH
O
Example
(52%)
+ CH3COH
O
O
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C C +
O
RCOOH
CC
O
+
O
RCOH
syn addition
Stereochemistry of Epoxidation
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peroxy acid
Give the structure of the alkene,including stereochemistry, that you wouldchoose as the starting material in a preparationof synthetic disparlure. Is disparlure chiral?
OH H
H H
Disparlureis chiral
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R
S R
S
Epoxidation of cis-2-Butene
syn addition to cis-2-butene gives meso diastereomer
RCO3H
meso
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The epoxidation of trans-2-butene produces:
A) A single enantiomerB) A product with one asymmetric carbon atomC) An optically inactive meso productD) A racemic mixtureE) 4 different stereoisomers each with 2 chiral
carbon atoms
Question
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ethylene H2C=CH2 1
propene CH3CH=CH2 22
2-methylpropene (CH3)2C=CH2 484
2-methyl-2-butene (CH3)2C=CHCH3 6526
More highly substituted double bonds react faster.Alkyl groups on the double bond make itmore “electron rich.”
Relative Rates of Epoxidation
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Question
Which reagent reacts with an alkene to produce an epoxide?
A) B)
C) D)
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Ozonolysis has both synthetic and analytical applications.
synthesis of aldehydes and ketonesidentification of substituents on the double bond of an alkene
Ozonolysis of Alkenes
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First step is the reaction of the alkene with ozone.The product is an ozonide.
+ O3 C CO
O O
C C
Ozonolysis of Alkenes
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Second step is hydrolysis of the ozonide. Two aldehydes, two ketones, or an aldehyde and a ketone are formed.
+ O3 C CO
O O
C C
C O CO+
H2O, Zn
Ozonolysis of Alkenes
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As an alternative to hydrolysis, the ozonide canbe treated with dimethyl sulfide.
+ O3 C CO
O O
C C
C O CO+
(CH3)2S
Ozonolysis of Alkenes
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1. O32. H2O, Zn
CH3
CH2CH3H
C C
CH2CH3
(38%) (57%)
CH2CH3
CO
CH2CH3
C O
CH3
H
+
Example
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A. A, C
B. A, D
C. A, E
D. B, C
E. B, E
Question
1) O32) DMS
O O
H
O
H
O
H
O
O
A. B. C.
D. E. F.
What are the products of the following reaction?
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Question
The ozonolysis of 2,4-dimethyl-2-pentene will produce:
A) B)
C) D)
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Introduction to OrganicChemical Synthesis
Planning Reaction Steps & Linking Reactions
MUST have a command of many reactions
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Question
H3O+
A. D.
B. E.
C.
1) Hg(OAc)2, H2O2) NaBH4
1) Hg(OAc)2, CH3OH2) NaBH4
1) Hg(OAc)2, CH3NH22) NaBH4
1) BH3.THF
2) H2O2, NaOH
OH
H
H OH
H OH
H
HO H
H
H
HO H
1. 5.
2. 6.
3. 7.
4. 8.
OCH3
NHCH3 CH3NH
a. A = 1; B = 4; C = 1; D = 1; E = 2, 6
b. A = 1; B = 8; C = 1; D = 6; E = 2, 6
c. A = 5; B = 4; C = 6; D = 1; E = 2, 6
d. A = 5; B = 8; C = 1; D = 6; E = 2, 6
e. A = 5; B = 4; C = 1; D = 1; E = 2, 6
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Example: trans vicinal diols
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A. KMnO4, NaOH, cold
B. 1) OsO4, pyridine 2) NaHSO3, H2O
C. 1) MCPBA 2) H3O+
D. OsO4 (catalytic), NMO
E. all of the above
Question
OH
OH
+ enantiomer
Which reagent(s) will produce the product in the following reaction?
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devise a synthetic planreason backward from the target moleculealways use reactions that you are sure will work
Prepare cyclohexane from cyclohexanol
OH
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ask yourself the key question"Starting with anything, how can I make cyclohexane in a single step by a reaction I am sure will work?"
Prepare cyclohexane from cyclohexanol
H2
Pt
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The only reaction covered so far for preparing alkanes is catalytic hydrogenation of alkenes.This leads to a new question. "Starting with anything, how can I prepare cyclohexene in a single step by a reaction I am sure will work?"
H2
Pt
Prepare cyclohexane from cyclohexanol
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Alkenes can be prepared by dehydration of alcohols.The synthesis is complete.
H2SO4
heatOH
H2
Pt
Prepare cyclohexane from cyclohexanol
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Question
A. E. I.
B. F. J.
C. G. K.
D. H. L.
1) MCPBA2) H3O+
OsO4 (catalytic), NMO
1) Hg(OAc)2, H2O2) NaBH4
1) BH3.THF
2) H2O2, NaOH
H2/Pt
Br2/H2O
Br2 NaOMe
O-
HBr
TsCl/pyridine
HBr/H2O2
BrOH
A. H, BB. H, CC. H, DD. I, BE. I, D
List the correct order of reagents to accomplish the following synthesis.
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Question
Which one of the following outlines the best synthesis of trans-2-chlorocyclohexanol?A) Heat a mixture of cyclohexanol and Cl2 to 400oC.B) 1. Treat cyclohexene with HCl;
2. Treat product of reaction 1 with peroxyacetic acid.C) 1. Hydrogenation of cyclohexene in the presence of Pt;
2. Treat product of reaction 1 with Cl2 in H2O.D) 1. Treat bromocyclohexane with KOC(CH3)3 in DMSO;
2. Treat product of reaction 1 with Cl2 in water.
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Question
Which one of the following is not stereospecific?A) reaction of cis-2-butene with peroxyacetic acidB) hydroboration-oxidation of 1-methylcyclopenteneC) addition of Br2 to trans-2-penteneD) addition of HBr to cis-2-butene in the
presence of peroxides
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Question
Which combination of reagents is the best choice for carrying out the conversion shown? A) 50% water - 50% sulfuric acidB) 1. H2SO4
2. H2O, heat
C) 1. O3
2. H2O, Zn
D) 1. BH3-THF
2. H2O2, NaOH