Epoxidation of Alkenes
are examples of heterocyclic compounds
three-membered rings that contain oxygen
ethylene oxide propylene oxide
H2C CH2
O
H2C CHCH3
O
Epoxides
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
cis-2-Methyl-7,8-epoxyoctadecane
Give the IUPAC name, including stereochemistry, for disparlure.
OH H
peroxy acid
C C +
O
RCOOH
CC
O
+
O
RCOH
Epoxidation of Alkenes
+ CH3COOH
O
Example
(52%)
+ CH3COH
O
O
C C +
O
RCOOH
CC
O
+
O
RCOH
syn addition
Stereochemistry of Epoxidation
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
R
S R
S
Epoxidation of cis-2-Butene
syn addition to cis-2-butene gives meso diastereomer
RCO3H
meso
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
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
Question
Which reagent reacts with an alkene to produce an epoxide?
A) B)
C) D)
Ozonolysis has both synthetic and analytical applications.
synthesis of aldehydes and ketonesidentification of substituents on the double bond of an alkene
Ozonolysis of Alkenes
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
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
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
1. O32. H2O, Zn
CH3
CH2CH3H
C C
CH2CH3
(38%) (57%)
CH2CH3
CO
CH2CH3
C O
CH3
H
+
Example
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?
Question
The ozonolysis of 2,4-dimethyl-2-pentene will produce:
A) B)
C) D)
Introduction to OrganicChemical Synthesis
Planning Reaction Steps & Linking Reactions
MUST have a command of many reactions
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
Example: trans vicinal diols
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?
devise a synthetic planreason backward from the target moleculealways use reactions that you are sure will work
Prepare cyclohexane from cyclohexanol
OH
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
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
Alkenes can be prepared by dehydration of alcohols.The synthesis is complete.
H2SO4
heatOH
H2
Pt
Prepare cyclohexane from cyclohexanol
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.
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.
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
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
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