Solvent- and Transition Metal Catalyst-Dependent Regioselectivity in the [3+2] Cyclocondensation of Trifluoromethyl<i>-</i>α,β<i>-</i>ynones with Hydrazines: Switchable Access to 3- and 5-Trifluoromethylpyrazoles
作者:Min-Tsang Hsieh、Sheng-Chu Kuo、Hui-Chang Lin
DOI:10.1002/adsc.201400853
日期:2015.3.9
The regioselectivity of the [3+2] cyclocondensation of trifluoromethyl‐α,β‐ynones with hydrazines can be readily tuned to preferentially afford either 3‐ or 5‐trifluoromethylpyrazoles through variation of the reaction conditions. Under catalysis with copper(II) acetate (2.0 mol%), cyclocondensation proceeded smoothly to yield 3‐trifluoromethylpyrazoles with high regioselectivity. In contrast, when
三氟甲基组成的[3 + 2]环化缩合反应中区域选择性- α,β - ynones与肼类可以容易地调谐到优先得到或者3-或通过反应条件的变化5- trifluoromethylpyrazoles。在乙酸铜(II)(2.0 mol%)的催化下,环缩反应顺利进行,得到具有高区域选择性的3-三氟甲基吡唑。相反,当反应在无催化剂的条件下在二甲基亚砜中进行时,主要观察到了5-三氟甲基吡唑的形成。