I read that the primary amine product of Gabriel Synthesis is a racemic mixture. However, when analyzing the reaction the stereochemical step(s) are all $S_N2$. Thus, I figured if you are careful you can track the stereochemistry of the (or both) $S_N2$ reaction(s). Can anyone clarify this for me?
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1$\begingroup$ As far as I remember, the Gabriel reaction transforms primary haloalkanes into primary amines. How do you attribute absolute configuration on a primary haloalkane of type $\ce{R-CH2-Br}$ to the Carbon atom just adjacent to the one of Bromine? $\endgroup$– ButtonwoodApr 3, 2017 at 23:13
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1$\begingroup$ @Buttonwood It works for secondary haloalkanes as well. For example, people use it to make amino acids which are secondary amines (with the exception of glycine). $\endgroup$– MasterYodaApr 7, 2017 at 0:42
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$\begingroup$ @Cocmos So far, my association with the synthesis of amino acids was the Strecker synthesis. Revisiting the Gabriel synthesis again, I found indeed an entry relevant to your welcomed comment, used in an answer below. The preparation of glycine with phtalimide, as outline in the Polish wikipedia about the same topic, indeed differs in its procedure. $\endgroup$– ButtonwoodApr 7, 2017 at 13:22
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The lower part of the Dutch wikipedia about the Gabrielsynthese indeed displays an example where this reaction is carried out to yield a secondary amine:
The original publication (DOI: 10.1021/jm9804376, J. Med. Chem., 1999, 42, 593-600) equally includes similar conversions with racemic secondary substrates like (R/S)-($\pm$)-1-methylpentyl bromide to yield (R/S)-($\pm$)-N-(1-methylpentyl)phthalimide which in turn was then converted into (R/S)-($\pm$)-(1-methylpentyl)amine hydrochloride.
answered Apr 7, 2017 at 13:18