Novel Chalcogen Bond Donors Derived from [3+2] Cycloaddition Reaction between 2-Pyridylselenyl Reagents and Isocyanates: Synthesis, Structures and Theoretical Studies

A novel [3+2] cycloaddition reaction between 2-pyridylselenyl halides or trifluoroacetates and isocyanates is described herein. This new convenient methodology allows the synthesis of novel 3-oxo-1,2,4-selenodiazolium scaffolds, which are inaccessible by the known methods. The coupling proceeds efficiently for a broad scope of substrates under mild conditions and allows preparation of cationic 3-oxo-1,2,4-selenodiazolium salts in high yields. The mechanism was analyzed using DFT calculations, evidencing the concerted nature of the novel cycloaddition reaction. The new Se-containing heterocycles were demonstrated to be structurally easily tunable donors of the chalcogen bonding (ChB). Noncovalent interactions in the solid state were studied using DFT calculations, molecular electrostatic potential surfaces and the quantum theory of atoms-in-molecules.