Back to basics: A transition‐metal‐free method developed for the synthesis of indazoles involves an inexpensive catalytic system composed of a diamine and K2CO3. Various (Z)‐2‐bromoacetophenone tosylhydrazones were converted into indazoles at room temperature in excellent yields (see example; Ts=p‐toluenesulfonyl). The yield was improved by photoisomerization with UV light when E/Z isomeric mixtures
简而言之:为合成吲唑而开发的一种无过渡金属的方法涉及由二胺和K 2 CO 3组成的廉价催化体系。各种(Z)-2-溴苯乙酮甲苯磺酰hydr在室温下均以优异的收率转化为吲唑(请参见示例; Ts =对甲苯磺酰基)。当使用原料的E / Z异构体混合物时,通过UV光进行光致异构化提高了产率。
Z-Selective synthesis of o-bromoacetophenone N-tosylhydrazones and formation of 3-methylindazoles in aqueous ethanol
A practical and effective Z-selective synthesis of o-bromoacetophenone N-tosylhydrazones is developed. Subsequent cyclization of Z-tosylhydrazones to furnish 3-methylindazoles is accomplished with the aid of copper and DMEDA in aqueous ethanol. Cyclization reactions are complete at ambient temperature in 10 min to afford the desired compounds in excellent yields.