Exercício de Química Sintética e Organica Mista (438)

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(c)
17.13 (b) Here we see an example of the Wittig reaction applied to diene synthesis by use of an ylide
containing a carbon–carbon double bond.
(c) Methylene transfer from methylenetriphenylphosphorane is one of the most commonly used
Wittig reactions.
17.14 A second resonance structure can be written for a phosphorus ylide with a double bond between
phosphorus and carbon. As a third-row element, phosphorus can have more than 8 electrons in its
valence shell.
17.15 (b) Two Wittig reaction routes lead to 1-pentene. One is represented retrosynthetically by the
disconnection
The other route is
1-Pentene
CH3CH2CH2CH CH2 �
Formaldehyde
O
HCH
Butylidenetriphenylphosphorane
CH3CH2CH2CH
��
P(C6H5)3
�
1-Pentene
CH3CH2CH2CH CH2 CH3CH2CH2CH
O
Butanal Methylenetriphenyl-
phosphorane
� �
CH2(C6H5)3P
Methylenetriphenylphosphorane
(C6H5)3P CH2CH2(C6H5)3P
� �
CCH3
O
Cyclohexyl methyl
ketone
CCH3
CH2
2-Cyclohexylpropene
(66%)
� �
Triphenylphosphine
oxide
O
�
(C6H5)3P
�
Methylenetriphenyl-
phosphorane
(C6H5)3P
�
CH2
�
�
Allylidenetriphenylphosphorane 1,3-Heptadiene (52%) Triphenylphosphine
oxide
Butanal
CH3CH2CH2CH CH3CH2CH2CH
O
(C6H5)3P CH2 CH2CHCHCHCH � (C6H5)3P O
�
��
�
Carbinolamine
intermediate
1-Piperidino-1-
phenylethene
PiperidineAcetophenone
C6H5CCH3
O
H
C6H5CCH3
OH
�H2O
C6H5C CH2
N
NN
ALDEHYDES AND KETONES: NUCLEOPHILIC ADDITION TO THE CARBONYL GROUP 433