Synthesis of pyrimidine-containing 3-aminobutenolides

An efficient synthesis of pyrimidine-containing butenolides is reported, starting from C-alkoxycarbonyl isoxazolidines. Two competitive reaction routes are operating: the pathway leading to homo-N,O-nucleosides, based on the reduction of an ester group at C₃, and the reaction channel leading to butenolides promoted by the removal of the hydrogen atom at C₃. The two reaction pathways can be easily controlled according to the adopted experimental conditions