Chiral sulfides, dioxirane oxidation

Chiral sulfides, dioxirane oxidation, 1156-7 Chlamydomonas reinhardtii, hydrogen peroxide determination, 646 y-Chlordene, isomers, 728 Chlorellajusca, hydrogen peroxide determination, 646... 

The enantioselective oxidation of prochiral sulfides with DMD has been achieved by using bovine serum albumin (BSA) as the chiral inductor Moderate to good enan-tioselectivities have been reported in the presence of this protein, for which a typical example is shown in equation 22 . As yet, however, no enantioselective oxidation of a prochiral sulfide has been documented by employing an optically active dioxirane. We have tried the enantioselective oxidation of methyl phenyl sulfide with the dioxirane generated from the ketone 7 (Shi s ketone), but an ee value of only ca 5% was obtained. One major hurdle that needs to be overcome with such enantioselective dioxirane oxidations is the suppression of the background oxidation of the sulfide substrate by Caroate, an unavoidable feature of the in-situ mode. 

Steric effects were responsible for the complete diastereocontrol observed in the oxidation of various 6-halopenicillins by dimethyl dioxirane (DMD). Only one of the two possible diastereomeric sulfoxides has been obtained in each case23 (Table 1). Scheme 3 shows that perborate oxidation of optically active sulfide 16 affords, with moderate diastereoselectivity (78% de), the (f )-sulfoxide 17,24 designed as chiral ligand for catalytic asymmetric synthesis. 

The oxidation of organic compounds with dioxirane reagents has emerged as an important synthetic method [93,94,95]. The effective use of dimethyldioxirane and methyl(trifluoromethyl)dioxirane for the mild and efficient oxidation of olefins, sulfides, amines, and saturated hydrocarbons naturally raised the question whether chiral versions of these reagents can be developed. 

Oxone sulfoxidations can show appreciable diastereoselectiv-ity in appropriate cases, as demonstrated in eq 26. Enantio-selective oxidations of sulfides to sulfoxides have been achieved by buffered aqueous Oxone solutions containing bovine serum albumin (BSA) as a chiral mediator (eq 27). As little as 0.05 equiv of BSA is required and its presence discourages further oxidation of the sulfoxide to the sulfone. Oxone can be the active oxidant or reaction can be performed in the presence of acetone, trifluoroacetone, or other ketones, in which case an intermediate dioxirane is probably the actual oxidizing agent. The level of optical induction depends on structure of the sulfide and that of any added ketone. Sulfoxide products show ee values ranging from 1% to 89%, but in most examples the ee is greater than 50%. 

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