Synthesis of 2-organylselanylbenzo[b]calcogenophenes via intramolecular cyclization of vinyl selenides

The 1,1-dibromoalkenes are a versatile building block in organic synthesis, which is widely applied in several transformations.1 We describe here a metal-free and selective method for the synthesis of (E)-1-bromo-1-seleno alkenes by a stoichiometric and temperature-controlled reaction. These protocols employ a diverse array of 1,1-dibromoalkenes and different diaryl diselenides to afford the corresponding products 3 in good yields and in a short reaction time. Having obtained the vinyl selenides 3, our next task was to study the best reaction conditions to prepare 2-organylselanylbenzo[b]calcogenophenes 4 by copper-catalyzed intramolecular cyclization. Thus, the best reaction condition to the cyclization of the substrate 3a (CuBr as catalyst, in a loading of 15 mol%, MeNO2 as solvent, under argon atmosphere and refluxing condition, for 24 hours) produced the desired product 4a in 90%. Other respective products 4b-i were obtained in good to excellent yields under this condition.