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. A dual catalytic approach combining photocatalyst and selenium‐π‐acid synergy for the cyclization of N‐propargylamides to oxazole aldehydes is disclosed, wherein vinyl selenium and hydroperoxide are involved as the key intermediates.