One‐Pot Synthesis of Novel Fluorescent 2 <i>H</i> ‐Dipyrazolo[1,5‐ <i>a</i> :4′,3′‐ <i>c</i> ]Pyridines

ABSTRACT In this study, the effective synthesis of novel 2 H ‐dipyrazolo[1,5‐ a :4′,3′‐ c ]pyridine derivatives is described. 3‐Alkynylpyrazole‐4‐carbaldehydes, p ‐toluenesulfonyl hydrazide, and an acidic α‐hydrogen atom‐containing aldehyde, ketone, or nitrile were combined in a silver (I)‐catalyzed one‐pot reaction to afford 2 H ‐dipyrazolo[1,5‐ a :4′,3′‐ c ]pyridine compounds with substituents at the 2‐, 5‐, 8‐, and 9‐positions. The scope of the system was further expanded to 4‐substituted derivatives by synthesizing 4‐iodo‐2‐phenyl‐2 H ‐dipyrazolo[1,5‐ a :4′,3′‐ c ]pyridine through a reaction containing pyrazole‐4‐carbaldehyde, p ‐toluenesulfonyl hydrazide, iodine, and an acidic α‐hydrogen atom‐containing aldehyde, and subsequently performing Suzuki cross‐coupling with aryl boronic acids. The structural assignments of the obtained compounds were based on 1 H‐, 13 C‐, and 15 N‐NMR, IR spectroscopy, high‐resolution mass spectrometry, and X‐ray crystallography. The photophysical properties of the obtained compounds were investigated using UV–vis and fluorescence spectroscopy.