I want to know the mechanism or some explanation as to how the last step here (with hydroxylamine) works:

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  • $\begingroup$ But why for example hydroxylamine doesn`t attack chlorine as nucleophillic substitution to give OH group back there? It would make much more sense as chlorine seems to be more reactive then some ester bond. @Waylander $\endgroup$ – Juraj Naroda Nov 24 '17 at 16:06
  • $\begingroup$ I can't definitively answer that except to observe that the major product is the hydroxamic acid. What I don't know is what the yield of this reaction is, attack on the chloromethyl could be a byproduct. $\endgroup$ – Waylander Nov 24 '17 at 16:24
  • $\begingroup$ C-Cl bond is strong, chloride is poor leaving group - these are factors that may contribute to its relative lack of reactivity under these conditions. Obviously, these are only back-rationalisations. $\endgroup$ – orthocresol Nov 24 '17 at 18:26

The hydroxylamine attacks the methyl ester through nitrogen giving the intermediate hydroxamic acid. The oxygen to the hydroxamic acid then attacks the chloromethyl to displace chlorine giving cycloserine.


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