Selenocyanation of Indoles Promoted by Visible-Light

We developed a promising synthetic methodology for the photo-regioselective 3-selenocyanation of indole employing potassium selenocyanate (KSeCN) and blue LED light, as a green alternative energy source. Derivatives of the indole organoselenium-substituted at the C3 position have emerged as a potentially bioactive molecules and already have demonstrated anti-inflammatory, antinociceptive and anticancer properties. There are in the literature several methodologies described for their preparation, for example, applying intermolecular cyclization with electrophilic selenium species. Therefore, it is of interest to seek innovative, robust and effective methodologies to selectively access this class of molecules.Furthermore, the photocatalytically formed NCSe^• radical can react directly with the N-heterocycle unsaturated substrates, affording the desired compound more effectively than other electrophilic selenium species. In addition, the 3-selenocyanato-1H-indole derivatives can be effective precursors for obtaining diselenides, through a reduction-oxidation sequence. The new method employs indole as unsaturated N-heterocycle substrate, and 1.3 equiv. of potassium selenocyanate, as selenium source, in the presence of 5.0 mol% of eosin Y, an organic photocatalyst, and 1.0 mL of acetonitrile. The system was stirred and irradiated with blue LED light for 5 hours, and the crude was purified using column chromatography. Thus, as a result, we have developed an efficient and smoothly methodology to prepare 3-selenocyanato-1H-indole derivatives, in good yields.