Synthesis and absolute configuration of optically active selenoxides. X-Ray molecular structure of (–)_se-4-menthyloxycarbonylphenyl 2,4,6-tri-isopropylphenyl selenoxide

Abstract

Enantiomerically pure, stable 4‐(methoxycarbonyl)phenyl selenoxide (‐)‐(VII) is isolated by fractional recrystallization of diastereoisomeric 4‐((‐)menthyloxycarbonyl)phenyl selenoxide (V) followed by removal of the chiral source.

Optically Active Selenoxides: Structural and Synthetic Aspects

“…A similar oxidation of the selenide 75 gave, with slight asymmetric induction (de = 7.6%), diastereoisomeric 4-[(-)-menthyloxycarbonyl] phenyl 2,4,6-tri-t-butyphenyl selenoxides 77a-b. Fractional crystallization of this diastereoisomeric mixture gave a sample of the levorotatory diastereoisomer 77a having de = 31.1% (estimated by measurement of the 77 Se NMR spectrum) [45]. The levorotatory enantiomer of 4-[(-)-methoxycarbonyl] phenyl 2,4,6-tri-iso propyl phenyl selenoxide 78 was obtained by transesterification of diastereoisomerically pure…”

“…On the other hand, transesterification of the levorotatory diastereoisomer 77a (de = 31.1% ) with sodium methoxide in methanol gave a sample of the selenoxide 79 with 29% ee. s Its washing with hexane left a solid that showed only 13% ee, while a sample of the selenoxide 79 isolated from the hexane solution exhibited a much higher enantiomeric excess (80%) [45]. at room temperature (Scheme 14).…”

“…The absolute configuration of the levorotatory enantiomer of selenoxide 78 was established to be S, taking into accounts the result of X-ray crystallographic analysis of the diastereoisomerically pure, levorotatory selenoxide 76a and the lack of inversion of configuration around the stereogenic selenium atom during the transesterification from (-)-(S se )-76 to methyl esters (-)-78 (Scheme 14) [45]. This determination was also supported by the presence of negative Cotton effects at the same wavelength region (284 nm) in the circular dichroism CD spectra of (-)-(76) and (-)-(78).…”

“…On the other hand, transesterification of the levorotatory diastereoisomer 77a (de = 31.1%) with sodium methoxide in methanol gave a sample of the selenoxide 79 with 29% ee. s Its washing with hexane left a solid that showed only 13% ee, while a sample of the selenoxide 79 isolated from the hexane solution exhibited a much higher enantiomeric excess (80%)[45]. The dehydration conversion of enantiomerically pure selenoxide (-)-78 (p-toluenesulfonamide (TsNH 2 ) / dicyclohexylcarbodiimide (DCC)/ 4-(dimethylamino)pyridine (DMAP)//80 • C) in 1,1,2-trichloroethane gave optically active 4-(methoxycarbonyl) phenyl(2,4,6-triisopropylphenyl)selenonium (N-toluene-4-sulfon)imide (-)-80 in 29% chemical yield.…”

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

“…For the past two decades, we and other research groups have succeeded in isolating optically active selenoxides, which were kinetically stabilized by bulky substituents [9][10][11][12]. 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].…”