Synthesis of 1, 3, 5-trisubstituted-4,5-dihydro-1H-pyrazole catalyzed by vitamin B1 and its fluorescence properties

Abstract An efficient synthesis of 1,3,5-trisubstituted-1 H -pyrazoles was developed via cyclocondensation in 78–92% yields starting from α , β -unsaturated aldehydes/ketones with substituted phenylhydrazine using vitamin B 1 as a catalyst, and was characterized by HR-MS, FT-IR, 1 H NMR and 13 C NMR spectroscopy. The reaction has simple operation, metal-free catalysis, acid or base free catalysis. As a green catalyst, vitamin B 1 was found to possess favorable catalytic activity and reusability for the condensation reaction. 1,3,5-trisubstituted-1 H -pyrazole shows from orange-red to cyan in different solvents when the electron withdrawing group is attached to acetophenone (taking compound 5i as an example). Compound 5i as a metal ion fluorescent probe has excellent selectivity for Ag + detection. The crystal structure of the compound 3-(4-chlorophenyl)-1,5-diphenyl-4,5-dihydro-1 H -pyrazole ( 5b ) in the orthorhombic space group Pca 21 was presented and formed racemic crystals. Graphical abstract