Iron(III) Chloride‐Promoted Cascade Cyclization of Diynylaryl Ethers With Diorganyl Diselenides for the Synthesis of Dibenzo‐Selenopheno‐Oxepines

A strategy for the synthesis of dibenzo‐selenopheno‐oxepines through the cyclization of 1,3‐diynylaryl ethers promoted by iron(III) chloride and diorganyl diselenides is described. The transformation proceeds under FeCl 3 ‐mediated conditions using dibutyl diselenide as the selenium source, affording the desired fused selenium‐containing heterocycles in moderate‐to‐good yields. Optimization studies revealed that the reaction strongly depends on the reaction medium, temperature, and the presence of 4 Å molecular sieves, which play a crucial role in suppressing side‐product formation and improving selectivity. Mechanistic investigations involving radical scavengers and control experiments support a nonradical ionic pathway initiated by electrophilic selenium activation of the alkyne. The process proceeds regioselectively via a sequential 7‐endo‐dig/5 ‐ endo‐dig cyclization, affording dibenzo‐selenopheno‐oxepines as the exclusive products.