A highly efficient heterogeneous palladium-catalyzed cascade three-component reaction of acid chlorides, terminal alkynes and hydrazines leading to pyrazoles

• The first heterogeneous palladium-catalyzed synthesis of pyrazoles is described.
• The MCM-41-2N–Pd(OAc)2 complex exhibits higher catalytic activity than PdCl2(PPh3)2.
• This palladium catalyst can be reused for 10 times without any decrease in activity.
• Our catalytic system provides a practical route for the synthesis of pyrazoles.

In the presence of 0.5 mol% of 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-2N–Pd(OAc)2] and 1.0 mol% of CuI, acid chlorides were coupled with terminal alkynes in Et3N at 50 °C to give α,β-unsaturated ynones, which were converted in situ into pyrazoles by the cycloaddition of hydrazines at room temperature with acetonitrile as cosolvent. The cascade reactions generated a variety of pyrazole derivatives in moderate to good yields, and this heterogeneous palladium catalyst exhibited higher catalytic activity than PdCl2(PPh3)2 and could be recovered and reused for at least 10 consecutive trials without any decreases in activity.

Figure optionsDownload as PowerPoint slide