Chemoselective Cyclization of 3-Phenyl-2-propynenitrile with 2-Pyridylselenenyl Chloride: Synthesis and Crystal Structure

Abstract

The reaction of 2-pyridylselenenyl chloride with 3-phenyl-2-propynenitrile proceeds under mild conditions to afford 3-(phenylethynyl)-[1,2,4]selenadiazolo[4,5-a]pyridin-4-ium chloride in 81% yield. The transformation exhibits exclusive chemoselectivity for the C≡N bond over the C≡C triple bond. The molecular structure of the product was unambiguously confirmed by single-crystal X-ray diffraction, revealing a planar bicyclic selenadiazolium core and a co-crystallized dichloromethane molecule. The crystal packing is governed by a cooperative network of noncovalent interactions, featuring bifurcated Se···Cl chalcogen bonds (2.867–2.916 Å) and C–H···Cl hydrogen bonds (2.615–2.649 Å) that form a robust supramolecular chelating motif with the chloride anion. Density functional theory calculations and QTAIM analysis provide quantitative insight into the nature and strength of the observed noncovalent interactions, confirming the presence of attractive chalcogen bonds.