Synthesis and Photoreaction of 2-Amino-3-cyano-4-aryl-4H-pyrans

A series of 2-amino-3-cyano-4-aryl-4H-pyrans (1) were synthesised by reacting malononitrile, ethyl acetoacetate, and aromatic aldehydes under ultrasound irradiation. The photochemical properties, including the photostability and photoreaction of 1, were investigated in conventional solvents. The results indicated that compounds 1 were unstable and underwent a photoreaction to the 1,3-butadienes under irradiation with UV light. A mechanism for the photoreaction is proposed and investigated using electron spin resonance spectroscopic techniques. The 1,3-butadiene structures were determined by 1H and 13C NMR spectra, high-resolution mass spectrometry, and single crystal X-ray diffraction analysis.