Post on 20-Dec-2015
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