Chelate ring size effect on the reactivity of [2-(2-phenyl-5,6-dihydro-4h-1,3-oxazinyl)]lithium and Se···N interactions in low-valent organoselenium compounds: facile isolation of diorganotriselenide

Abstract

The reaction of [2-(2-phenyl-5,6-dihydro-4H-1,3-oxazinyl)]lithium (13), containing a six-membered oxazine ring, with elemental selenium gave lithium aryldiselenolate (14) as the major reaction intermediate along with other polyselenolates (15 and 16), whereas [2-(4,4-dimethyl-2-phenyloxazolinyl]lithium (21), containing a five-membered oxazoline ring, on reaction with selenium gave only lithium arlyselenolate 22 under similar conditions. The unusual selenation reaction of aryllithium 13 has been studied by ES-MS spectrometry. The oxidative workup of in situ-generated lithium arylpolyselenolates (14-16) afforded a mixture of diorganopolyselenides (10, 11, 17, and 18), from which diorganotriselenide 11 was obtained as the major product, whereas lithium arylselenolate 22 gave only diselenide 6 on oxidation. Equimolar reactions of diorganotriselenide 11 with sulfuryl chloride and benzenethiol give the novel selenium halide [RSeSeCl (24)] and seleniumselenenyl sulfide (28), respectively. However, the reaction of triselenide 11 with an excess amount of halogenating reagents afforded selenenyl halides [RSeX; X=Cl (25), Br (26), I (27)]. The reaction of lithium arylpolyselenolates (14-16) with benzyl chloride gave a mixture of diselenide (10), unsymmetrical diselenide (31), benzyl selenide (32), and dibenzyl diselenide (33). The reaction of 14-16 with α,α'-dibromo-ortho-xylene gave the 10-membered diselenocine (34) and 26. GPx-like activities of diselenide 10 and triselenide 11 have been evaluated by using both benzenethiol and coupled reductase assay methods. Triselenide 11 shows much better GPx-like activity than diselenide 10. Crystal structures of organoselenium compounds (11, 25-27, 29, 32, and 34) were determined by single X-ray crystallography to study the ring size effect of the oxazine ring on Se···N intramolecular interactions.