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。