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852 CHAPTER 21 
 
location between the two carbonyl groups, and the  
position bears the keto group: 
 
 
 
Since the two partners are different, we use a crossed 
Claisen condensation. LDA is used as the base in the 
first step, and the final step of the process is aqueous 
acidic work-up, as shown: 
 
 
 
(d) We first identify the  and  positions, and then 
apply a retrosynthetic analysis. The  position is the 
location between the two carbonyl groups, and the  
position bears the keto group: 
 
 
 
Since the two partners are different, we use a crossed 
Claisen condensation. LDA is used as the base in the 
first step, and the final step of the process is aqueous 
acidic work-up, as shown: 
 
 
 
 
(e) We first identify the  and  positions, and then 
apply a retrosynthetic analysis. The  position is the 
location between the two carbonyl groups, and the  
position bears the keto group: 
 
 
 
Since the two partners are different, we use a crossed 
Claisen condensation. LDA is used as the base in the 
first step, and the final step of the process is aqueous 
acidic work-up, as shown: 
 
 
 
 
21.27. 
(a) This is an example of an intramolecular Claisen 
condensation (called a Dieckmann cyclization). The  
position of one ester group is deprotonated, and the 
resulting enolate functions as a nucleophile and attacks 
the other carbonyl group within the same structure. As a 
result, a ring is formed, giving a tetrahedral intermediate. 
The carbonyl group is then reformed via loss of an 
ethoxide ion, giving a -ketoester: 
 
 
 
Under these basic conditions, the -ketoester is 
deprotonated to give a doubly-stabilized enolate, 
requiring acidic work-up in order to regenerate the -
ketoester above. 
 
 
 
(b) This is an example of an intramolecular Claisen 
condensation (called a Dieckmann cyclization). The  
position of one ester group is deprotonated, and the 
resulting enolate functions as a nucleophile and attacks 
the other carbonyl group within the same structure. As a 
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