Efficient synthesis of substituted pyrazoles Via [3+2] cycloaddition catalyzed by lipase in ionic liquid

In this work, an enzymatic method for the de novo construction of diverse substituted pyrazoles from readily available diazo compounds and alkynoates/allenoates in ionic liquids was established. Under the optimum reaction condition (3-alkynoates or allenoates (0.5 mmol), diazo compounds (0.6 mmol), [BMIM][PF6] (2 mL), C. rugosa lipase (15 mg), 45 °C, 8 h.), pyrazoles bearing different groups were obtained in satisfactory yields (61 %−93 %). The method features a diversity of substituents of the pyrazole products and remarkably simple work-up.