A ionic hydrogenation of aryl-substituted 4H-selenopyrans

Abstract

Aryl-substituted 4H-thiopyrans readily undergo catalytic and ionic hydrogenation [1]. Their seleno analogs readily eliminate elemental selenium in attempts to perform catalytic and other traditional methods of hydrogenation [2]. Aryl-substituted selenacyclohexanes were obtained and characterized upon the disproportionation of 4H-selenopyrans under acid catalysis conditions [3].We are the first to report the ionic hydrogenation of 2,4,6-triaryl-4H-selenopyrans 1 and 2 to give the corresponding 2,4,6-triarylselenacyclohexanes. Se Ph Ph Se Ph Ph 1, 2 C 6 H 4 R-p CF 3 COOH HSiEt 3 3, 4 C 6 H 4 R-p 1, 3 R = H; 2, 4 R = OMeGC/MS analysis of the reaction mixture indicated that the isomer content of the sample of 2,4,6-triphenylselenacyclohexane (3) obtained by ionic hydrogenation was identical to the isomer content of the product obtained by disproportionation [3] and contained more than 97% of one isomer, while the second isomer was present as an impurity. (p-Methoxyphenyl)-2,6-diphenyl-4-selenacyclohexane (4) was obtained as a mixture of four isomers; the content of the major isomer was about 70%. Selenacyclohexane 4 obtained by disproportionation contained more than 90% major isomer.The GC/MS analysis of the samples was carried out on an HP5890/5972 unit equipped with an HP-5MS capillary column. The injector temperature was 200°C. The onset time was 3 min. The onset temperature was 50°C. The final temperature was 280°C, ∆T = 10°C/min. Helium served as the gas carrier, v = 1 ml/min. The 1 H NMR spectra were obtained at 30°C on a Varian FT 80A spectrometer at 80 MHz in CDCl 3 using TMS as the internal standard.