α,β-Unsaturated Carbonyl Compounds

C OCC conjugated system

CH2=CHCH=O

acrolein

CH2=CHCOOH

acrylic acid

H2C CHC N

acrylonitrile

H2C C

CH3

COOH

methacrylic acid

CH3CH=CHCH=O

crotonaldehyde

O

mesityl oxide

CH

CH

CH=O

cinnamaldehyde

CH

CH

C

O

benzalacetophenone chalcone

C

C

C

CH

HO

O

OH

OH

maleic acid

C

C

C

HC

HO

OH

O

HO

fumaric acid

O

O

O

maleic anhydride

α,β-Unsaturated Carbonyl Compounds, reactions:

1. electrophilic addition

deactivated

2. nucleophilic addition

activated

3. Michael Addition

4. Diels-Alder Reaction

1. electrophilic addition

The carbonyl group is an electron withdrawing group when conjugated with a double bond. This decreases the electron density and deactivates the double bond to electrophilic addition.

C C C O + HZ C C C O

HZ

H2C CH

CH

OHCl

CH2CH2CHO

Cl

O CH3OH

H2SO4

O

OCH3

H2C CH

COOHH2O,H+

H2CH2C COOH

OH

C C C O + H C C C OH

electrophilic addition mechanism:

C C C OH

H

C C C O C C C OH H

more stable

C C C O + H C C C OH

electrophilic addition mechanism:

C C C OH

Z

C C C OH

C C C OHZ

Zunstable

enol

C C C O

Z H

2. nucleophilic addition

The carbonyl group is an electron withdrawing group when conjugated with a double bond. This decreases the electron density and activates the double bond to nucleophilic addition.

C C C O + Z- C C C O

HZ

H2O

CH

CH

COOHNH2OH

CHCH2COOH

NHOH

O O

NHCH3

CH

CH

COOEtNaCN,aq. H

CH2C COOEt

CNH3C H3C

CH3NH2

C C C O C C C O

nucleophilic addition mechanism:

C C C O C C C OZ Z

more stable

+ Z

Z

Z

C C C O

nucleophilic addition mechanism:

C C C O C C C OZ Z

ZH

C C C O C C C OH

Z ZH

keto-enol tautomers

3. Michael Addition.

Carbanions as the nucleophiles in nucleophilic addition to α,β-usaturated carbonyls. (The enolate anion must be in reasonably high concentration for the Michael Addition to take place. Such enolates can be obtained from removal of alpha-hydrogens that are next to two electron withdrawing groups.)

CH

CH

C

O+

COOEt

CH2

COOEt

piperidine HC

H2C C

O

CHEtOOC COOEt

benzalacetophenone diethylamalonate

H2C C

CH3

COOEt +COOEt

CH2

C N

OEt

H2C CH

CH3

COOEt

CHCOOEtCN

HC C

HC

O

CH3 +

COOEt

CH2

C

O

CH3

base HC

H2C C

O

CH3

CHC COOEt

O

H3C

G

+

G

mechanism: (concerted)

G G

4. Diels-Alder reaction: diene + dienophile cyclohexene

+

CH=OO

1,3-butadiene acrolein

+ O

O

O

O

O

O

1,3-butadiene maleic anhydride

+

1,3-butadiene

O

O

O

O

p-benzoquinone

O

O

+ O

O

O

O

O

O

endo is preferred over the exo productany unsaturated groups in the dienophiletend to lie near the developing double bondin the diene rather than farther away (exo).

O

O

O

endo

exo

α,β-Unsaturated Carbonyl Compounds, reactions:

1. electrophilic addition

deactivated

2. nucleophilic addition

activated

3. Michael Addition

4. Diels-Alder Reaction

C C C O + HZ C C C O

Z H

+

C

O

C

O