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Alpha Alkylation

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    1156
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    Enolates can act as a nucleophile in Sn2 type reactions. Overall an α hydrogen is replaced with an alkyl group.  This reaction is one of the more important for enolates because a carbon-carbon bond is formed. These alkylations are affected by the same limitations as Sn2 reactions previously discussed. Good leaving groups like chloride, bromide, iodide, tosylate, should be used. Also, secondary and tertiary leaving groups should not be used because of poor reactivity and possible competition with elimination reactions. Lastly, it is important to use a strong base, such as LDA or sodium amide, for this reaction.  Using a weaker base such as hydroxide or an alkoxide leaves the possibility of multiple alkylation’s occurring. 

    Example 1: Alpha Alkylation

    Mechanism

    1) Enolate formation

     

    2) Sn2 attack

    Problems

    1) Please write the structure of the product for the following reactions.

     

     

    Answers

    1)

    Contributors

    William Reusch, Professor Emeritus (Michigan State U.), Virtual Textbook of Organic Chemistry