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

Abstract 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 ( 1 O 2 ), which is responsible for this transformation.