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　H-1　and　C-13　NMR　spectra,　high-resolution　mass　spectrometry,　and　single　crystal　X-ray　diffraction　analysis.