Mechanism and Stereochemistry of the luorination of Uracil and Cytosine Using Fluorine and Acetyl Hypofluorite

Article abstract of DOI:10.1021/jo00359a015

The products of the reaction of CH3COOF and F2 with uracil and cytosine dissolved in acetic acid and water were studied by using 18F as a tracer.Apart from 5-fluorouracil (2) and the 5,5-difluoro adducts 5a and 5b, the 1H NMR spectra of the crude reaction mixture showed the presence of two geometric isomers of both 5- fluoro-6-acetoxy-5,6-dihydrouracil (3a, 4a) and 5-fluoro-6-hydroxy-5,6-dihydrouracil (3b, 4b).In the fluorination of cytosine, corresponding products were observed with the exception of the acetoxy adducts.For both reagents and for both substrates a radical-cation mechanism is proposed.The observed conversions of the acetoxy adducts of uracil are explained by an acylimine (iii) as an intermediary.