Pyridazin-3(2H)-ones via D2-isoxazoline intermediates: synthetic studies

An efficient method for the prepn. of 6-​substituted-​4,​5-​dihydro-​3(2H)​pyridazinones I (R = alkyl, benzyl, etc.) was described. The synthetic strategy is based on Δ2-​isoxazolines chem. which were unmasked by N-​O bond cleavage and cyclized to the target compd. Utilizing the same approach was possible to obtain both 6-​substituted-​3(2H)​-​pyridazinones and 6-​substituted-​4-​hydroxy-​4,​5-​dihydro-​3(2H)​-​pyridazinones. This protocol was also extended to a C-​nucleoside starting from β-​ribofuranosylnitromethane. Moreover, an intramol. version of this methodol. has been developed to prep. a known antiulcer tricyclic 3(2H)​-​pyridazinone. The unusual transformation of compds. I into the corresponding 3-​(1-​naphthyl)​propionic acid Et ester derivs. was also reported.