Synthesis of Selenochromenes via Dehydration of Arylalkynols Promoted by Iron(III) Chloride and Diorganyl Diselenides.

We report here the regioselective 6--dig cyclization of [2-(butylselanyl)phenyl]propynols promoted by the cooperative action between diorganyl diselenides and iron(III) chloride leading to the formation of 4-methylene-3-(organoselanyl)-selenochromenes. The results of the reaction condition optimization studies showed that the solvent, the iron source, and the amount of diorganyl diselenide had a fundamental influence on the reaction yields. In the presence of iron(III) chloride (1.5 equiv) and diorganyl diselenides (1.0 equiv), using dichloromethane as the solvent, at room temperature, 4-methylene-3-(organoselanyl)-selenochromenes were formed in moderate to good yields. The reaction conditions were found to be suitable for substrates bearing electron-donating and electron-withdrawing groups on the aromatic ring at both propargyl and alkyne positions. However, we observed a limitation in the reaction conditions when they were applied to other diorganyl dichalcogenides, such as diorganyl disulfides and diorganyl ditellurides, which did not give the corresponding products. We also elaborated on a mechanism proposal based on control experiments performed.