Recyclable iodine-catalyzed radical selenylative annulation of 2-alkynyl biaryls with diselenides in water: a green approach to selanyl polycyclic aromatic hydrocarbons and polycyclic heteroaromatics

Herein, we disclose a metal-free, recyclable iodine-catalyzed, highly atom-economical, cost-effective, scalable, and sustainable oxidative selenylative annulation of 2-alkynyl biaryls and 2-heteroaryl-substituted alkynyl benzenes with diselenides in water for the synthesis of a wide variety of selanyl polycyclic aromatic hydrocarbons (PAHs) and polycyclic heteroaromatics, respectively, through the in situ formation of the corresponding selenyl iodide intermediates. The phenylselenyl iodide (PhSeI), formed in situ from (PhSe)₂ and I₂, is found to be more reactive than its other halo-analogues (commercially available), i.e., PhSeBr and PhSeCl, for the selenylative annulation of 2-alkynyl biaryls. Several synthesized products, i.e., selanyl phenanthrenes were further synthetically diversified to various new classes of interesting molecules. Both experimental and computational studies supported the radical pathway over the polar (ionic) pathway for the oxidative selenylative annulation of 2-alkynyl biaryls. Notably, 70-80% of the catalyst (iodine) was recovered after the reaction during the column chromatography stage and further the same was recycled for two successive runs without any compromise in the reaction outcome.