Abstract

1,3-Disubstituted-5-chloro-4-iodopyrazoles are selectively coupled with phenylacetylene under typical Sonogashira reaction conditions [PdCl₂(PPh₃)₂, CuI, Et₃N, dimethylformamide (DMF)] to obtain the corresponding 5-chloro-4-(phenylethynyl)pyrazoles in good yield. The latter are smoothly cyclized with Na₂S in DMF into the corresponding thieno[2,3-c]pyrazoles. Detailed spectroscopic investigations (¹H, ¹³C, and ¹⁵N NMR, mass, and infrared) of all compounds are reported.