甲基肼（Ⅳ）与乙氧次甲基丙二酸二乙酯（Ⅲ）环化缩合，生成两个异构体。５－羟基－１－甲基吡唑－４－羧酸乙酯（Ⅰ）和３－羟基－１－甲基吡唑－４－羧酸乙酯（Ⅱ）。研究了反应条件对（Ⅰ）和（Ⅱ）产率的影响，发现等摩尔的（Ⅲ）与（Ⅳ）在无水乙醇中反应，得到３３．８％的（Ⅰ）和５０．１％的（Ⅱ），而在弱酸性（ｐＨ＝３～４．）条件下，于７０％乙醇（水）溶液中反应，则得到６３％～６４％的（Ⅰ）和１９％～２０％的（Ⅱ）。同时测定了（Ⅰ）和（Ⅱ）的熔点、红外和１Ｈ核磁共振谙 Methyl hydrazine (IV) cyclizes with diethyl ethoxymethylenemalonate (III) to form two isomers. Ethyl 5-hydroxy-1-methylpyrazole-4-carboxylate (I) and ethyl 3-hydroxy-1-methylpyrazole-4-carboxylate (II). The effects of reaction conditions on the yields of (I) and (II) were investigated. It was found that equimolar amounts of (III) and (IV) reacted in absolute ethanol to give 33.8% (I) and 50.1% (II), and in 70% ethanol (water) at weak acidity (pH = 3-4), 63% to 64% of I and 19% to 20% ). The melting points of (Ⅰ) and (Ⅱ) were also determined. The infrared and 1H nuclear magnetic resonance spectra were also obtained