Organic fluorophores have been often utilized in the study of luminescence-based sensors. One fluorophore, dapoxyl sulfonic acid (DSA), has a unique excited state with a large dipole that directly impacts its solvent sensitivity. However, DSA is very costly, difficult to synthesize, and is limited to aqueous and highly polar solvents due to its inherent polarity. Given these disadvantages, the current study examines a preparation of DSA derivatives using a [3+2] cycloaddition between a terminal alkyne and an acyl azide under copper catalysis. Pérez recently reported this method to produce 2,5-diaryl oxazoles in high yields, with structures similar to DSA. However, none of the examples utilized an amino functional group. An interesting observation was found in our lab where the previously unreported 2,4-diaryl oxazole is isolated when the benzoyl azide contains a <i>para</i>-dimethylamino substituent and the copper(I) catalyst contains a hexafluorophosphate counteranion. The use of Pérez’s original tetrafluoroborate catalyst with the same benzoyl azide, only affords the 2,5-diaryl oxazoles. This indicates that the counteranion may be playing a role in the mechanism. Based on these prior results, the goal is to explore this unexpected byproduct and optimize regiochemical control by attaining a better understanding of the reaction mechanism. Ultimately, we aim to synthesize a small library of diverse DSA derivatives that can be examined as possible fluorophores.

Exploring regioselective oxazole formation through a transition metal complex catalyzed [3+2] cycloaddition reaction

251st National Meeting (2016)

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