epoxidation of alkenes

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?

Retrosynthesis

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