Chemistry of oxaziridines. 3. Asymmetric oxidation of organosulfur compounds using chiral 2-sulfonyloxaziridines

Abstract

Chiral2-sulfonyloxaziridines, 9-12, afford the best enantioselectivity of any chiral oxidizing reagent for the asymmetric oxidation of sulfides and disulfides to sulfoxides and thiosulfinates, respectively, 5-8 times better than chiral peracids. For asymmetric oxidations using 9-12, the configuration of the oxaziridine three-membered ring was shown to control the configuration of the product, which could be predicted using a chiral recognition mechanism (Figure 2). The increased asymmetric bias exhibited by chiral 2-sulfonyloxaziridines was attributed to the fact that the active-site oxygen was incorporated into a rigid chiral environment. The group size difference (GSD) effect in both the oxaziridine and substrate play important roles in determining the absolute configuration of the product and the magnitude of the asymmetric bias. As the GSD increases the enantioselectivity increases.

The oxidation of organic sulphides by Mortierellaisabellina. 2. Effects of substituents on the stereochemistry of sulphoxide formation

“…In spite of the continued interest in chiral sulphoxides, both in the study of sulphur stereochemistry (1) and as intermediates in asymmetric synthesis (2), the best direct chemical methods for their generation from sulphides (3) have not yet achieved the high degree of enantiomeric purity desirable in modem asymmetric synthesis. High enantiomeric excesses (>35%) are routinely available for p-tolyl alkyl sulphoxides (only) by a modification (4) of the Anderson synthesis (5) using sulfinate esters, or by the use of biological oxidizing agents employing sulphides as substrates.…”

Synthesis of enantioenriched sulfoxides

“…137 Highest enantioselectivity in this study was observed for the oxidation of sulfide 137 (Scheme 57). …”

“…The greatest degree of enantiocontrol was observed in the oxidation of tert-butyl sulfide 146, which was not surprising as investigations by Davis established that the stereocontrol exerted by the oxaziridine during the oxidation was due to steric effects (Scheme 61). 137 Sulfides that did not possess a sterically demanding group were less susceptible to stereocontrol during the oxidation.…”

Investigation of the chemoselective and enantioselective oxidation of α-thio-β-chloroacrylamides

“…Very efficient biological sulfide oxidations have been reported using both whole cell systems and isolated enzymes. 14,15 Metal-free asymmetric sulfur oxidation has been reported using oxaziridines 16 and hydroperoxides. 17 The most popular route to asymmetric sulfur oxidation is metal-catalysed oxidation.…”