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Alkylation of Imines: achiral to chiral compounds

  1. May 6, 2015 #1
    I found this in "March's Advanced organic chemistry"
    Untitled.png
    After that step, on using HCl in pentane, you will get 4-methyl-3-Heptanone.
    So this method was used to convert achiral 2-pentanone to a chiral compound, by first converting it to the compound on left by addition reaction and then using a 2 step process. On checking the appendix, its given that the reaction is alkylation of imines.
    Can someone give me the mechanism for alkylation of imines using iPr2NLi?
    And whats the use of pentane with HCl?
     
  2. jcsd
  3. May 6, 2015 #2

    TeethWhitener

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    iPr2NLi (also known as LDA) is a strong base, so start by figuring out what protons on the starting imine are going to be the most acidic. Maybe look up "enamines" to get an idea of why they're nucleophilic. Once you abstract a proton with LDA, you'll be left with a nucleophile which can attack the alkyl iodide in a standard nucleophilic substitution reaction.

    As for the pentane/HCl combo, there are a few different reasons why you'd want to use a biphasic system for the hydrolysis of the imine. My guess is that the ketone final product is preferentially soluble in pentane and the imine is preferentially soluble in water (aqueous HCl). Since imine hydrolysis is an equilibrium reaction, as the ketone is generated, it is pulled into the pentane solution, shifting the reaction further toward the ketone product.
     
  4. May 6, 2015 #3
    I know about LDA. It's also used in aldol condensation to produce thermodynamic enolate.
    It usually extracts proton from carbon right next to ketone group. Here it takes proton from aliphatic secondary carbon next to C=N group.
     
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