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I have included a short part from a synthetic pathway from: https://synarchive.com/syn/112

$\ce{Mg3N2}$ reacts with $\ce{MeOH}$ to liberate $\ce{NH3}$ which I believe is used in nucleophilic substitution at the esters and amides in the last step. However, before this, the designers of this reaction pathway added in TFAA, introducing new groups onto the amines. Why is this step necessary? Why can't the researchers just use $\ce{NH3}$ or $\ce{Mg3N2}$ right after $\ce{SOCl2}$ and $\mathrm{h\nu}$?

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  • $\begingroup$ I wondered about that one too. It seems unneccessary. Would need to read the full paper to see if there is an explanation. $\endgroup$
    – Waylander
    Commented Sep 13, 2021 at 10:13
  • $\begingroup$ Very interesting. I see that they do that trick in another step, too, the one where they replace I by CN using CuCN. Is it possible that those two NH2 groups on the fused Ph ring impart so much electron density to the system, that whenever you need to do a reaction where a nucleophile attacks, you need to subtract electron density first, in this case by attaching an electron-withdrawing acyl to the NH2 groups? Just a hypothesis though, might be something else entirely. $\endgroup$
    – user6376297
    Commented Sep 13, 2021 at 17:00
  • $\begingroup$ @user6376297 I note that they use sulfuric acid conditions to remove those trifluoroacetyl groups immediately before a KOH treatment to hydrolyse the methyl ester when (in my opinion) the KOH would easily remove them. A little odd! $\endgroup$
    – Waylander
    Commented Sep 13, 2021 at 18:54
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    $\begingroup$ I had a look at the paper - much simpler: it was because of solubility. They say that the free bis-amino compound is too insoluble in organic solvents to be purified on silica. $\endgroup$
    – user6376297
    Commented Sep 14, 2021 at 9:39

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