Sonogashira Coupling Offers a New Synthetic Route to Thieno[2,3-c]pyrazoles

Abstract

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.

Keywords:

• Fused-ring systems
• NMR spectroscopy
• palladium catalysis
• pyrazoles

ACKNOWLEDGMENTS

The authors are grateful to Dr. L. Jirovetz, University of Vienna, for recording the mass spectra. G. V. and E. A. thank the ERASMUS student exchange program for providing scholarships.