Regioselective Formation of Naphtho[2,1-b]selenophenes via Cascade Cyclization of 1,3-Diynylpropargyl Alcohols Promoted by Iron(III) Chloride and Diorganyl Diselenides

This manuscript reports a selective diorganyl diselenide/iron(III)-promoted strategy for the synthesis of selenium-containing heterocycles, specifically naphtho[2,1-b]selenophene derivatives, via cascade cyclization reactions.Using 1,3diynylpropargyl alcohols as key substrates and diorganyl diselenides as selenium sources, the optimized conditions involve iron(III) chloride and dibutyl diselenide in dichloromethane under an inert atmosphere at room temperature, followed by the addition of the substrate and stirring for 12 hours. A series of 25 novel derivatives was synthesized in good yields, demonstrating the scope and versatility of the protocol, which was also extended to include diorganyl disulfides. However, the optimized conditions did not work for diorganyl ditellurides, even when some reaction parameters were changed. The reaction mechanism insights are discussed, and the synthetic utility of the resulting heterocycles as intermediates in further transformations is showcased. This cascade process enables the formation of four new bonds (carbon-carbon, carbonselenium, selenium-carbon, and carbon-selenium) in a single reaction step.