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.
描述了一种从3,5-二取代的4,5-二氢异噁唑出发,高效制备6-取代的3(2H)-吡嗪酮和6-取代的4,5-二氢-4-羟基-3(2H)-吡嗪酮的方法。通过六羰基钼或催化氢化促进异噁唑啉环的N-O键断裂,获得了α-羟基γ-酮酯4a-f,这些酯在室温或回流条件下与水合肼反应生成6-取代的4,5-二氢-4-羟基-3(2H)-吡嗪酮5a-f或6-取代的3(2H)-吡嗪酮6a-f,且收率较高。该协议的灵活性通过从已知的β-核糖硝基甲烷8合成C-核糖苷7得到了验证。此外,还开发了一种分子内版本的方法来制备已知的抗溃疡三环3(2H)-吡嗪酮12。