Benzeneseleninic acid was used under visible light irradiation (white LEDs) to promote the oxidative cyclization of N-propargyl amides to the respective 2-substituted oxazole-5-carbaldehydes. A total of twelve 2-aryl oxazole-5-carbaldehydes, six of them so far unprecedented, were prepared in 30-90 % yield in just 1 hour of reaction at room temperature. No metal catalysts, nor strong oxidants or heating were necessary, making this a mild method to access a valuable class of compounds. The only co-products are water and diphenyl diselenide, that can be recovered and converted to new benzeneseleninic acid for a new reaction.
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