Exercício de Química Sintética e Organica Mista (488)

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(d ) Conversion of 3-pentanone to 3-hexanone requires addition of a methyl group to the �-carbon
atom.
The best way to add an alkyl group to the � carbon of a ketone is via conjugate addition of a
dialkylcuprate reagent to an �,�-unsaturated ketone.
(e) The compound to be prepared is the mixed aldol condensation product of 3-pentanone and
benzaldehyde.
The desired reaction sequence is
18.25 (a) The first step is an � halogenation of a ketone. This is customarily accomplished under condi-
tions of acid catalysis.
In the second step the carbonyl group of the �-bromo ketone is reduced to a secondary
alcohol. As actually carried out, sodium borohydride in water was used to achieve this
transformation.
(CH3)3CCCH2Br
O
1-Bromo-3,3-dimethyl-2-butanone 
(CH3)3CCHCH2Br
OH
1-Bromo-3,3-dimethyl-2-butanol (54%)
NaBH4
H2O
(CH3)3CCCH3
O
3,3-Dimethyl-2-butanone
(CH3)3CCCH2Br
O
1-Bromo-3,3-dimethyl-2-butanone (58%)
Br2
H�
CH3CCCH2CH3
O
C6H5CH
2-Methyl-1-phenyl-
1-penten-3-one
CH3CHCCH2CH3
O
C6H5CHOH
Aldol addition product
(not isolated; dehydration
occurs under conditions
of its formation)
CH3CH2CCH2CH3
O
3-Pentanone
CH3CHCCH2CH3
O
Enolate of 3-pentanone
HO� �H2OC6H5CH
�
O
C6H5CH
O
�CH3CHCCH2CH3CH3CCCH2CH3
O
C6H5CH
2-Methyl-1-phenyl-
1-penten-3-one
O
�
1-Penten-3-one
[prepared as described in part (b)]
H2C CHCCH2CH3
O
3-Hexanone
O
CH3CH2CH2CCH2CH3
1. LiCu(CH3)2
2. H2O
CH3CH2CH2CCH2CH3
O O
H2CCH3 � CHCCH2CH3
�
�
ENOLS AND ENOLATES 483