First example of aromatic electrophilic substitution using selenium(II) chloride

Abstract

Selenium dichloride is a promising reagent for organic synthesis. However, prior to our studies [1, 2], it was not used for the preparation of organoselenium compounds. It is known that selenium dichloride in solution exists in equilibrium with selenium tetrachloride and Se2Cl2 [3]. No examples of aromatic electrophilic substitution with participation of selenium dihalides have been reported so far. While continuing our systematic studies on reactions of selenium dihalides [1, 2, 4–10], we examined the reaction of selenium dichloride with methoxybenzene. The reaction occurred as aromatic replacement of hydrogen by the electrophile Se and afforded bis(4-methoxyphenyl) selenide (I) in high yield (91%). Thus selenium dichloride may be used as source of electrophilic Se species in aromatic electrophilic substitution reactions. The possibility of using selenium dihalides for performing analogous reactions with other aromatic systems is now under study. Bis(4-methoxyphenyl) selenide (I). mp 54–55°C; published data [11]: mp 54°C. H NMR spectrum, δ, ppm: 7.28 d (4H, CH, J = 7.4 Hz), 6.69 d (4H, CH, J = 7.4 Hz), 3.72 s (6H, CH3O). C NMR spectrum, δC, ppm: 158.85 (C), 135.24 (C), 122.04 (C), 114.53 (C), 54.49 (CH3O). Mass spectrum, m/z (Irel, %): 294 [M] (75), 214 (100), 199 (96), 187 (14), 171 (28), 144 (12), 128 (25), 107 (77), 92 (13), 77 (14), 63 (47), 39 (18). The H and C NMR spectra were recorded on a Bruker DPX-400 spectrometer at 400.13 and 100.61 MHz, respectively, from a solution in carbon tetrachloride; the chemical shifts were determined relative to hexamethyldisiloxane. The mass spectrum (electron impact, 70 eV) was obtained on a Shimadzu GCMS-QP5050A instrument.