The iron-promoted tandem cyclization-functionalization reaction of N-arylpropargylamines with diorganyl diselenides was developed for the preparation of 3-(organoselanyl)-1,2-dihydroquinolines. The best result was obtained when the reaction of N-arylpropargylamines was carried out by the combination of diorganyl diselenides with FeCl 3 · 6H 2 O in nitromethane at 70 8C. The control experiments strongly support the cooperative relation between the iron salts and diorganyl diselenides and their high reactivity not only to promote the cyclization but also to introduce a functionalization at the 3-position of dihydroquinolines. The results indicate the existence of an iron/diorganyl diselenide complex, which forms both a cation and an anion of organoselenyl. In an attempt to prove the synthetic application of 3-(organoselanyl)-1,2-dihydroquinolines prepared, we evaluated their use as substrates in the transition metal-catalyzed cross-coupling reactions with nucleophiles, such as boronic acids.

A practical synthetic approach to the synthesis of 3-(organoselenyl)-imidazothiazines was developed. The methodology involved the regioselective 6-endo-dig cyclization of thiopropargyl benzimidazoles promoted by diorganyl diselenides and iron­(III) chloride. The investigation to determine the best reaction conditions indicated the use of thiopropargyl benzimidazoles (0.25 mmol) with diorganyl diselenides (1.0 equiv) and iron­(III) chloride (2.0 equiv) in dichloromethane at 40 °C for 30 min to be optimal. Under these conditions, the scope of the substrates was evaluated varying the structures of thiopropargyl benzimidazoles and diorganyl diselenides giving 28 3-(organoselenyl)-imidazothiazines in moderate to good yields. The reaction conditions were also applicable to diorganyl ditellurides; however, they did not work for diorganyl disulfides. The mechanism studies were carried out indicating that the cyclization proceeds via a cooperative action of diorganyl diselenides and iron­(III) chloride, but a direct electrophilic cyclization, promoted by the in situ formed electrophilic organoselenium species, cannot be ruled out.