AuCl₃-Catalyzed Synthesis of 5-Bromomethyl Oxazoles from Amino Acids

Significance

Reported is the one-pot synthesis of 5-bromomethyl oxazoles by sequential gold(III)-catalyzed cyclization of amino acid derived propargyl amides to form intermediate A, followed by bromination to give the observed products in good yield. This work builds upon the results of Hashmi who developed the AuCl₃-catalyzed cyclization to form oxazoles from amides (e.g., A. S. K. Hashmi., J. P. Weyrauch, W. Frey, J. W. Bats Org. Lett. 2004, 6, 4391). However, both Hashmi and the current authors found the reaction fails when non-terminal alkynes are used. The present method overcomes this limitation by intercepting a reactive intermediate (observed using ^¹H NMR spectroscopy during the cyclization by the Hashmi group) to form a reactive bromide.