Preparation
In addition to the original procedure shown above (which may have compatibility issues for sensitive substrates), Weinreb amides can be synthesized from a variety of acyl compounds. The vast majority of these procedures utilize the commercially available salt N,O-dimethylhydroxylamine hydrochloride, which is typically easier to handle than the free amine.
Treatment of an ester or lactone with AlMe3 or AlMe2Cl affords the corresponding Weinreb amide in good yields. Alternatively, non-nucleophilic Grignard reagents such as isopropyl magnesium chloride can be used to activate the amine before addition of the ester.
A variety of peptide coupling reagents can also be used to prepare Weinreb-Nahm amides from carboxylic acids. Various carbodiimide-, hydroxybenzotriazole-, and triphenylphosphine- based couplings have been reported specifically for this purpose.
Finally, an aminocarbonylation reaction reported by Stephen Buchwald allows conversion of aryl halides directly into aryl Weinreb-Nahm amides.
Read more about this topic: Weinreb Ketone Synthesis
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