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
Synthesis of 4-Fluoromethylsydnones and their Participation in Alkyne Cycloaddition Reactions
作者:Robert S. Foster、Harry Adams、Harald Jakobi、Joseph P. A. Harrity
DOI:10.1021/jo400381a
日期:2013.4.19
We report the synthesis and some structural studies of 4-trifluoromethyl, 4-difluoromethyl-, and 4-monofluoromethylsydnones. All but the latter compounds are stable and represent effective precursors to a range of pyrazoles after cycloadditionreactions with alkynes. The cycloadditions are generally highly regioselective and provide 5-fluoromethylpyrazole products, although we have observed that Bn-substituted