title: Unusual photochemical transformation of 5-ethylorotate to 5-ethylidenehydroorotate.
abstract: Ultraviolet irradiation of 5-ethylorotate in aqueous medium led to formation of 5-ethylidenehydroorotate via a 1,3-hydrogen rearrangement from the ethylene group of the 5-substituent to the ring C6. The same product was also obtained by an alternate pathway via a hitherto unidentified intermediate. The structure of this unusual pyrimidine analogue, established in the solid state by X-ray diffraction, was shown with the aid of spectroscopic methods to be the same in solution, and some of its properties are described. Heating of 5-ethylidenehydroorotate in the solid state led by direct conversion to a mixture of the parent 5-ethylorotate and 5-ethyluracil. By contrast, ultraviolet irradiation in aqueous medium resulted in quantitative photochemical conversion of the photoproduct to 5-ethyluracil.
mesh_terms: D006358:Hot Temperature; D009682:Magnetic Resonance Spectroscopy; D009963:Orotic Acid / Q000031:analogs & derivatives* / Q000528:radiation effects; D011743:Pyrimidines; D013054:Spectrophotometry, Atomic; D013056:Spectrophotometry, Ultraviolet; D014466:Ultraviolet Rays
chemical_list: D011743:Pyrimidines; D009963:Orotic Acid