The breitfussins are halogenated natural products whose structures were determined with the assistance of atomic-force microscopy. The site selectivity of N-bromosuccinimide-mediated bromination of a model breitfussin core was found to be strongly dependent on solvent selection; use of acetone led to oxazole bromination, and use of a pyridine-containing mixture led to pyrrole bromination. This tunable site-selective bromination was used in a protecting-group-free synthesis of breitfussin B that proceeded in 9.2% yield over 12 reactions and five chromatographic separations. A bromooxazole analogue of breitfussin A was also prepared by late-stage bromination but isomerized on silica gel to form breitfussin B. This isomerization appeared to proceed through a unimolecular pathway.
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Reprinted (adapted) with permission from Org. Lett., 2015, 17 (15), pp 3718–3721. Copyright 2015 American Chemical Society.