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[摘要]：The ring-opening mode of the title oxazolones with hydrazide nucleophiles was investigated from both synthetic and mechanistic points of view. The novel ring opening proceeded to give (Z)-2-(3-methyl-5-substituted 1,2,4-triazol-4-yl)-3-aryl-2-propenoates [1,2,4-triazole-substituted (Z)-a-dehydroarylalanines] as major products, along with minor or negligible amts. of their isomers. Substituent and solvent effects on the relative compn. of these 2 isomers confirmed that this compn. was dependent on steric and electronic factors of the aryl (in the oxazolones) and acyl (in the hydrazide nucleophiles) substituents as well as on solvent polarity. MM2 and PM5 calcns. provided a strong piece of evidence in support of the mechanism, in which the triazole ring is constructed via the preferential nucleophilic addn. of the hydrazino N to the C:N double bond in the oxazolone ring. |
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