Regioselective Three‐Component Synthesis of Highly Fluorescent 1,3,5‐Trisubstituted Pyrazoles

Abstract

Abstract 3,5‐Disubstituted and 1,3,5‐trisubstituted pyrazoles are readily synthesized from acyl chlorides, terminal alkynes, and hydrazines by a consecutive one‐pot three‐component Sonogashira coupling/Michael addition/cyclocondensation sequence in good to excellent yields. These pyrazoles are highly fluorescent, both in solution and in the solid state. Investigation of the electronic properties by UV/Vis and fluorescence spectroscopy and by DFT and ZINDO CI computations reveal that the excited state is highly polar and allows fine‐tuning of the absorption and emission properties. X‐ray structure analyses of 3,5‐disubstituted pyrazoles reveal self‐organization by hydrogen bonding and π‐stacking. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)