Exocyclic N-Acyliminium Ion (NAI) Cyclization: Access to Fully Substituted Oxazoles and Furocoumarins

A concise, one-pot route to oxazoles and furocoumarins has been reported. The key step in this transformation involves in situ generation of N-acyliminium ion (NAI) precursor under catalyst and solvent-free conditions and their further transformations promoted by superacid in the same pot. We have also presented the experimental evidence for the involvement of proto-solvated novel exocyclic N-acyliminium ion. Further, the UV–visible and fluorescence studies revealed that few of the compounds reported here exhibited emission of blue light upon irradiation in EtOH in the region of 404–422 nm.