1. 6.18 Epoxidation of Alkenes

2. are examples of heterocyclic compounds
Epoxides
are examples of heterocyclic compounds
three-membered rings that contain oxygen
ethylene oxide propylene oxide
H2C
CH2 O
H2C
CHCH3 O 2

3. Substitutive nomenclature: named as epoxy-substituted alkanes.
Epoxide Nomenclature
Substitutive nomenclature: named as epoxy-substituted alkanes.
“epoxy” precedes name of alkane
1,2-epoxypropane 2-methyl-2,3-epoxybutane 1
CHCH3 O C
H3C 2 3 4
H2C
CHCH3 O 2

4. cis-2-Methyl-7,8-epoxyoctadecane
Problem Give the IUPAC name, including stereochemistry, for disparlure. O H
cis-2-Methyl-7,8-epoxyoctadecane 5

5. Epoxidation of Alkenes
RCOOH C +
peroxy acid O
RCOH C O + 6

6. Example
+ CH3COOH O
+ CH3COH O O
(52%) 7

7. Stereochemistry of Epoxidation
RCOOH C +
syn addition O
RCOH C O + 6

8. Problem Give the structure of the alkene, including stereochemistry, that you would choose as the starting material in a preparation of synthetic disparlure. O H 9

9. Problem Give the structure of the alkene, including stereochemistry, that you would choose as the starting material in a preparation of synthetic disparlure. H
peroxy acid O H 9

10. 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.” 6

11. Mechanism of Epoxidation6

12. 6

13. 6

14. Ozonolysis has both synthetic and analytical applications.
6.19 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 15

15. Ozonolysis of Alkenes
First step is the reaction of the alkene with ozone. The product is an ozonide. C C O
+ O3 17

16. 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
H2O, Zn C O C O + 17

17. Ozonolysis of Alkenes
As an alternative to hydrolysis, the ozonide can be treated with dimethyl sulfide. C C O
+ O3
(CH3)2S C O C O + 17

18. Example CH3 CH2CH3 H C 1. O3 2. H2O, Zn CH2CH3 C O C O CH3 H + (38%)
(57%) 19