23-2. Carbonyl Condensations vs. α Substitutions

　今回は 23-2. カルボニル縮合反応とα置換反応の比較 を要約したいと思います。

 This theme is 23-2. Carbonyl Condensations vs. α Substitutions.

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23-2. Carbonyl Condensations versus Alpha Substitutions

 Carbonyl condensations and alpha substitutions occur under the similar experimental condition.  Both of them need a base, and proceed by enolate ion intermediates.  How can we carry out one of them selectively?

◎Alpha Substitutions

 In alpha-substitution reactions, we normally use a full equivalent of strong base to convert all carbonyl compounds into enolate ions.  Then, any condensation reactions can't occur, because no unreacted carbonyl compounds is left.  Also, the conversion takes place rapidly at low temperature.  The enolate ion reacts with an electrophile as soon as it is added.

ex)

◎Carbonyl Condensation
 Carbonyl condensation reactions need only a catalytic amount of a relatively weak base.  When the base is added, a small amount of enolate ion is yielded.  And, it reacts with an unreacted carbonyl compound: condensation reacions.  Then, the basic catalyst is regenerated.

ex)

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　以上、 23-2. カルボニル縮合反応とα置換反応の比較 でした。
　次回は 23-3. アルドール生成物の脱水：エノンの合成 を要約します。

 23-2. Carbonyl Condensations versus Alpha Substitutions has finished.
 I'm going to summarize 23-3. Dehydration of Aldol Products: Synthesis of Enones for next entry.