Photocatalytic Aerobic Cyclization of N‐Propargylamides Enabled by Selenium‐π‐Acid Catalysis

A dual catalytic approach combining photocatalyst and selenium-π-acid synergy has been used to cyclized of N-propargylamides. This method offers readily access to oxazole aldehydes under chemical oxidant-free conditions with low catalyst loadings, where air acts as a terminal and gratuitous oxidant. The reaction is demonstrated with a range of substrates, including aryl and alkyl propargyl amides, and in the late-stage functionalization of several amide-containing drug molecules. Mechanistic studies suggest that the acridinium catalyst is able to oxidize diselenide and generate singlet oxygen (1O2), which is responsible for this transformation.