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.

Structural aspects of some organoselenium compounds

“…For 7 the chemical shift is close to that observed for the corresponding selenenylsulfide derived from 4,4-dimethyl-2-phenyl-2-oxazoline (576 ppm) [13]. However, the chemical shift for 7 is significantly upfield shifted compared to the corresponding selenenylsulfide (625 ppm) derived from 2-pheny-2-oxazine [3]. The spiroselenurane 8 was obtained serendipitously during the protonation of selenaazamacrocycles with phosphoric acid [14].…”

“…The Se···N bond distance is slightly longer than the selenenylsulfide based on 4,4-dimethyl-2-phenyl-2-oxazoline [2.617(2) Å] having a five-membered heterocyclic ring [17]. On the other hand, the Se···N distance in 7 is significantly larger than the selenenylsulfide of 2-phenyl-2-oxazine [2.458(2) Å] having a six-membered heterocyclic ring [3]. The Se − S bond distance and C − Se − S angle [2.213(6) Å and 101.80 (7) • ] are comparable to the corresponding bond length and angle reported for related selenenylsulfides.…”

“…Our group has studied the thiol peroxidase-like activities of a series of intramolecularly coordinated diorganodiselenides where the donor atom is nitrogen [1][2][3][4]. The diselenide (1) without any Se···N intramolecular interaction exhibits better thiol peroxidase-like activity compared to the diselenide (2), which has a strong Se···N interaction.…”

“…Organoselenenylsulfides have been proposed as intermediates in the catalytic cycle of glutathione peroxidase mimics [1][2][3][4][5][6][7]. Very few stable and structurally characterized selenenylsulfides are reported in literature.…”

Synthesis and characterization of novel trans-3-benzyl/(diphenyl)methyl/naphthyl seleno substituted monocyclic β-lactams: X-ray structure of trans-1-(4′-methoxyphenyl)-3-(diphenyl)methylseleno-4-(4′-methoxyphenyl)azetidin-2-one

“…The SeeC bond length between Se and C-3 of b-lactam 6b [SeeC (14), 1.94 A] lie within the range (1.90e1.95 A), reported for several organoseleno compounds possessing SeeC bond [38,39]. However, the SeeC bond length between Se and methine carbon atom of (diphenyl)methyl is slightly longer i.e., [SeeC(1), 1.99 A], indicating the weakening of CeSe bond as a result of another phenyl substitutient.…”