Nitrile Oxide [3 + 2] Cycloaddition: Application to the Synthesis of 6-Substituted 3(2H)-Pyridazinones and 6-Substituted 4,5-Dihydro-4-hydroxy-3(2H)-pyridazinones
Nitrile Oxide [3 + 2] Cycloaddition: Application to the Synthesis of 6-Substituted 3(2H)-Pyridazinones and 6-Substituted 4,5-Dihydro-4-hydroxy-3(2H)-pyridazinones
prepared using Schiff's bases derived from aromatic aldehydes and amines or α-aminoesters. These complexes are versatile catalyst for the reaction between aliphatic aldehydes and various alkenes. The outcome of the reaction is controlled by the electronic nature of the alkene as the electron deficient alkenes undergo oxidative addition of aldehydes followed by dioxygen incorporation to yield 2-hydr
Nitrile Oxide [3 + 2] Cycloaddition: Application to the Synthesis of 6-Substituted 3(2<i>H</i>)-Pyridazinones and 6-Substituted 4,5-Dihydro-4-hydroxy-3(2<i>H</i>)-pyridazinones
作者:P. G. Baraldi、A. Bigoni、B. Cacciari、C. Caldari、S. Manfredini、G. Spalluto
DOI:10.1055/s-1994-25663
日期:——
An efficient method for the preparation of 6-substituted 3(2H)-pyridazinones and 6-substituted 4,5-dihydro-4-hydroxy-3(2H)-pyridazinones starting from 3,5-disubstituted 4,5-dihydroisoxazoles is described. N-O bond cleavage of the isoxazoline ring promoted by molybdenum hexacarbonyl or by catalytic hydrogenation afforded the α-hydroxy γ-keto esters 4a-f which were converted into 6-substituted 4,5-dihydro-4-hydroxy-3(2H)-pyridazinones 5a-f or 6-substituted 3(2H)-pyridazinones 6a-f on treatment with hydrazine hydrate at room temperature or reflux in high yield starting from 4a-f. The flexibility of this protocol has been demonstrated by the synthesis of the C-nucleoside 7 starting from the known β-ribofu-ranosylnitromethane 8. Moreover, an intramolecular version of this methodology has been developed to prepare the known antiulcer tricyclic 3(2H)-pyridazinone 12.