Epoxidation of Alkenes
Epoxides
are examples of heterocyclic compounds
three-membered rings that contain oxygen
ethylene oxide
CH2
H2C
O
propylene oxide
CHCH3
H2C
O
Epoxide Nomenclature
Substitutive nomenclature: named as
epoxy-substituted alkanes.
“epoxy” precedes name of alkane
1,2-epoxypropane
2-methyl-2,3-epoxybutane
1
H3C
O
3
H3C
4
CHCH3
C
CHCH3
H2C
2
O
Give the IUPAC name, including
stereochemistry, for disparlure.
H
O
H
cis-2-Methyl-7,8-epoxyoctadecane
Epoxidation of Alkenes
O
C
C
+
RCOOH
peroxy acid
O
C
C
O
+
RCOH
Example
O
+ CH3COOH
O
+ CH3COH
O
(52%)
Stereochemistry of Epoxidation
O
C
C
+
RCOOH
syn addition
O
C
C
O
+
RCOH
Give the structure of the alkene,
including stereochemistry, that you would
choose as the starting material in a preparation
of synthetic disparlure. Is disparlure chiral?
H
H
peroxy acid
H
O
H
Disparlure
is chiral
Epoxidation of cis-2-Butene
R
S
RCO3H
S
R
meso
syn addition to cis-2-butene gives meso diastereomer
Question
The epoxidation of trans-2-butene produces:
A) A single enantiomer
B) A product with one asymmetric carbon atom
C) An optically inactive meso product
D) A racemic mixture
E) 4 different stereoisomers each with 2 chiral
carbon atoms
Relative Rates of Epoxidation
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 it
more “electron rich.”
Question
Which reagent reacts with an alkene to produce
an epoxide?
A)
C)
B)
D)
Ozonolysis of Alkenes
Ozonolysis has both synthetic and analytical
applications.
synthesis of aldehydes and ketones
identification 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.
C
C
+ O3
O
C
O
C
O
Ozonolysis of Alkenes
Second step is hydrolysis of the ozonide.
Two aldehydes, two ketones, or an aldehyde
and a ketone are formed.
C
C
O
+ O3
C
O
C
O
H2O, Zn
C
O
+
O
C
Ozonolysis of Alkenes
As an alternative to hydrolysis, the ozonide can
be treated with dimethyl sulfide.
C
C
O
+ O3
C
O
C
O
(CH3)2S
C
O
+
O
C
Example
CH2CH3
CH3
C
C
H
CH2CH3
1. O3
2. H2O, Zn
CH2CH3
CH3
C
O
H
(38%)
+
O
C
CH2CH3
(57%)
Question
What are the products of the following reaction?
1) O3
2) DMS
A.
B.
O
C.
O
O
H
D.
E.
O
H
F.
O
A. A, C
B. A, D
O
H
C. A, E
D. B, C
E. B, E
Question
The ozonolysis of 2,4-dimethyl-2-pentene will
produce:
A)
C)
B)
D)
Introduction to Organic
Chemical Synthesis
Planning Reaction Steps & Linking Reactions
MUST have a command of many reactions
Question
A.
1) Hg(OAc)2, CH3OH
2) NaBH4
1) Hg(OAc)2, H2O
D. 2) NaBH4
1.
5.
OH
B.
1) Hg(OAc)2, CH3NH2
2) NaBH4
E.
1) BH3.THF
2) H2O2, NaOH
OCH3
HO H
H OH
2.
6.
H
H
C.
H3O+
a. A = 1; B = 4; C = 1; D = 1; E = 2, 6
H OH
3.
d. A = 5; B = 8; C = 1; D = 6; E = 2, 6
e. A = 5; B = 4; C = 1; D = 1; E = 2, 6
7.
H
b. A = 1; B = 8; C = 1; D = 6; E = 2, 6
c. A = 5; B = 4; C = 6; D = 1; E = 2, 6
HO H
H
4.
8.
NHCH3
CH3NH
Example: trans vicinal diols
Question
Which reagent(s) will produce the product in the following reaction?
OH
+ enantiomer
OH
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
Retrosynthesis
Prepare cyclohexane from
cyclohexanol
OH
devise a synthetic plan
reason backward from the target molecule
always use reactions that you are sure will
work
Prepare cyclohexane from
cyclohexanol
H2
Pt
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?"
Prepare cyclohexane from
cyclohexanol
OH
H2SO4
H2
heat
Pt
Alkenes can be prepared by dehydration of
alcohols.
The synthesis is complete.
Question
List the correct order of reagents to accomplish the following synthesis.
Br
OH
A.
1) MCPBA
2) H3O+
E.
Br2
I.
B.
OsO4 (catalytic), NMO
F.
H2/Pt
J.
HBr
C.
1) Hg(OAc)2, H2O
2) NaBH4
G.
Br2/H2O
K.
TsCl/pyridine
D.
1) BH3.THF
2) H2O2, NaOH
H.
L.
HBr/H2O2
O-
NaOMe
A. H, B
B. H, C
C. H, D
D. I, B
E. I, D
Question
Which one of the following outlines the best synthesis of trans-2chlorocyclohexanol?
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
acid
B) hydroboration-oxidation of 1methylcyclopentene
C) addition of Br2 to trans-2-pentene
D) 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 acid
B) 1. H2SO4
2. H2O, heat
C) 1. O3
2. H2O, Zn
D) 1. BH3-THF
2. H2O2, NaOH