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

We report here the
regioselective 6-endo-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.