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18.4: 19.4 New Synthesis of Aldehydes and Ketones

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    183093

    • Ester, Acid Chloride, and Nitrile Reduction to form Aldehydes

    The reduction of esters, acid chlorides, and nitriles require reducing agents that are derivatives of lithium aluminum hydride (LiAlH4).  For esters and nitriles, LiAlH4 is modified into the organometallic reagent diisobutyl aluminum hydride which can be represented as DIBAL or DIBAL-H or DIBAH or DIBALH.  To reduce acid chlorides, t-butoxide groups are combined with LiAlH4 to form lithium tritert-butoxy aluminum hydride.  

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    Carboxylic Acids can be converted to Aldehydes

    Carboxylic acids cannot be reduced directly to aldehydes.  Carboxylic acids can be converted to acid chlorides using thionyl chloride which can then be reduced to aldehydes using LiAlH(O-t-Bu)3.

    ch 19 sect 4 example 1.png

    Grignard reagents react with Nitriles to form Ketones

    Nitriles can also be used to synthesize ketones when they react with Grignards as shown below.

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    Organocuprate reagents react with Acid Chlorides to form Ketones

    Organocuprate reagents are the least reactive of the organometallic reagents studied so far.  While we learned to synthesize alcohols by reacting Grignard reagents with aldehydes and ketones, organocuprates will not react with aldehydes and ketones. 

    Grignard reagents will keep reacting with the product of the acid chloride reaction. 

    ch 19 sect 4 example 2.png

    Organocuprate reactions with acid chlorides stop at the ketone as shown below.

     ch 19 sect 4 example 3.png

    Exercise

    3. Complete the reaction map below.

    ch 19 sect 4 exercise.png

    Answer

    3.

    ch 19 sect 4 exercise solution.png

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