N-Acylated dehydroamino acid esters are easily accessible in two steps from a wide variety of aromatic aldehydes and hippuric acid. These esters have been used for the preparation of e. g. chiral amino acids and dihydro-oxazoles and are naturally occurring building blocks of peptides. The aim of this work is to explore the versatility of the reaction of N-protected dehydroamino acid esters with N-bromo succinimide (NBS). This reaction has been used in the synthesis of halo-, hydroxy-, and alkoxy-amino acid derivatives. Specifically, it has been used for the preparation of substituted oxazoles from N-benzoylamino acid esters. Under the conditions employed in this work, the formation of substituted oxazoles and other heterocyclic compounds was observed when treating N-acylated dehydroamino acid esters with NBS. Dependent upon the nature of the aromatic aldehyde used in the synthesis of the dehydroamino acid derivative and the reaction conditions employed, brominated and halogen-free products as well as oxidation products were observed. Mechanistic studies suggest multi-step processes leading to heterocycles. Reactions were monitored by time-resolved 1H-NMR spectroscopy.

Reactions of N-acylated dehydroamino acid esters with N-bromo succinimide

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