Optical Resolution and Configurational Stability of Selenoxides Stabilized by Intramolecular Coordination

Abstract

2-((Dimethylamino)methyl)phenyl alkyl (or aryl) selenoxides, configurationally stabilized by intramolecular coordination of an amino group to the selenium atom, were optically resolved into their enantiomeric isomers by means of high-performance liquid chromatography using an optically active column packed with amylosecarbamate derivative/silica gel. This is the first example of the isolation of optically pure selenoxides without bulky substituents and also the first isolation of optically pure alkyl aryl selenoxides. The absolute configuration of the (-)-isomers could be assigned to be the S-form by comparison of their specific rotations, circular dichroism spectra, and behavior on the optically active column with those of the sulfur analogue, prepared by Andersen's method. Racemization of the optically active selenoxides was accelerated not only in acidic solution but also in basic media. This result indicates there are two different mechanisms for their racemization in acidic and basic media. The stabilization energy of the selenoxides by the intramolecular coordination of an amino group to the selenium atom was estimated to be ca. 3 kcal mol(-)(1) on the basis of variable-temperature (1)H NMR measurements.

Stabilizing effect of intramolecular lewis base toward racemization of optically active selenoxides

“…3. These Cotton effects corresponded with those of (S)-(−)-4a-c [14]. Therefore, the absolute configurations of selenoxides (−)-2a-c were assigned to be S-form and those of (+)-2a-c were R-form.…”

“…We have also succeeded in isolating optically active selenoxides with 2-(N,Ndimethylaminomethyl)phenyl group [13], which were stabilized by intramolecular coordination of amino group to the selenium atom (thermodynamic stabilization) [14].…”

Structure and dynamic behavior of neutral hexacoordinate antimony compounds with intramolecular coordination

“…Reversed-phase liquid chromatography (RPLC) was performed using a JAI LC-928 instrument (Japan Analytical Industry Co., Ltd., Tokyo, Japan). 1-Bromo-2-(methoxymethyl)benzene [9], 1-bromo-2-(dimethylaminomethyl)benzene [10], and 1-bromo-2-(2-pyridyl)benzene [11] were prepared by literature methods.…”

Thermodynamically stabilized chiral chalcogen oxides: optical resolution and stereochemistry

“…Diaryl selenides 3b and 3c and tellurides 5a and 5b were also synthesized by reacting the lithium reagent 4 with the corresponding diselenides or ditellurides in yields of 46, 41, 49, and 11%, respectively. Finally, racemic selenoxides 1a, 1b, and 1c and telluroxides 2a and 2b were obtained in 82-98% yields by oxidation [19,22] of the corresponding selenides or tellurides with tert-butyl hypochlorite, followed by treatment with aqueous sodium hydroxide.…”

“…For example, reactive and unstable divalent organoselenium and tellurium compounds [7][8][9][10][11][12][13][14][15][16][17][18], such as selenenyl [7][8][9][10][11] and tellurenyl [12][13][14][15][16][17][18] halides, selenolates [7,[9][10][11], and tellurolates [12][13][14][15][16][17][18], have been isolated by using the stabilization by intramolecular coordination. Recently, we reported the isolation of optically active selenoxides [19] and telluroxides [20] possessing the 2-(N,N-dimethylaminomethyl)phenyl group; however, their configurational stabilities were not satisfactory in solutions, although the intramolecular coordination of the amino group to the chalcogen atoms certainly retarded the racemization.…”