Boronate facilitates conversion of an ester to an amide

What is it about?

In the study of amide bond forming reactions of an amine adjacent to a boronic acid, we observed unexpected reaction with an ester solvent (ethyl acetate). It appears to require the electron-withdrawing effect of a boronate-salicylate ester. A dative bond between the boron and the amide carbonyl oxygen creates a spirocyclic system with interesting intereactions in the solid state.

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Why is it important?

We believe the manner in which this reaction occurs may be applicable to other functional group transformations. In fact, we have recently published an example of amidine formation that it is facilitated by boronate exter formation. See Pappin, et al. Organic & Biomolecular Chemistry 2019, vol. 17, p. 803.