Sulfoxides Dimethyldioxirane

In general, peroxomonosulfates have fewer uses in organic chemistry than peroxodisulfates. However, the triple salt is used for oxidizing ketones (qv) to dioxiranes (7) (71,72), which in turn are useful oxidants in organic chemistry. Acetone in water is oxidized by triple salt to dimethyldioxirane, which in turn oxidizes alkenes to epoxides, polycycHc aromatic hydrocarbons to oxides and diones, amines to nitro compounds, sulfides to sulfoxides, phosphines to phosphine oxides, and alkanes to alcohols or carbonyl compounds. 

The use of dimethyldioxirane in the oxidation reactions of sulfides deserves to be mentioned [83, 84] as this mild neutral oxygen transfer reagent allows, for instance, highly reactive compounds such as a-oxosulfones to be obtained. Although the oxidation can usually be controlled at the sulfoxide level by using a stoichiometric amount of the... 

Butyl hypochlorite, 55 of phenols to quinones Benzoyl /-butyl nitroxide, 28 2,3-Dichloro-5,6-dicyano-l, 4-benzoqui-none, 104 Periodic acid, 238 of phosphorus compounds Dimethyldioxirane, 120 of selenium compounds Potassium permanganate, 258 of sulfides to sulfoxides and sulfones /-Butyl hydroperoxide-Dialkyl tar-trate-Titanium(IV) isopropoxide, 51 ra-Chloroperbenzoic acid, 76, 112 Dimethyldioxirane, 120 of thiols to sulfur compounds Trimethylsilyl chlorochromate, 327... 

Chemical shift data (toluene-r/8) for the sulfoxides and sulfones obtained from the oxidation of 3-arylide-nethiochroman-4-ones using dimethyldioxirane are shown in Table 9 <2003MRC193>. 

Determination of dimethyldioxirane concentration by the GLC method is as follows A standard solution of thioanisole (phenyl methyl sulfide) is prepared. The solution is usually 0.2 M in acetone, but other concentrations may be used. It is important to keep the sulfide in excess so that oxidation by the dioxirane will produce largely or exclusively the sulfoxide and not the sulfone. 

To determine the dioxirane concentration 1 mL each of the dioxirane, sulfide, and internal standard solutions are combined in a vial. The GLC analysis is then carried out using the following Column DB 210 temp 1 = 60°C, time 1 = 5 min. rate 1 20°/min temp 2 = 200°C, time 2 = 5 min. The analysis is conducted on 1 pL of solution. The analysis is made quantitative by determining the response factors of the sulfide and internal standard in the usual manner. The dimethyldioxirane concentration is determined by measuring the sulfide concentration before and after adding the dioxirane. Under these conditions the following retention times are observed dodecane, 7.15 min sulfide, 8.2 min sulfoxide, 12.9 min. 

FIGURE 3.1 Thermodynamic oxygen transfer potentials. DMDO, dimethyldioxirane Ac, CH3C(0) DMSO, dimethyl sulfoxide DMS, dimethyl sulfide. 

Oxidation of Sulfur Functional Groups. Dimethyldioxirane rapidly oxidizes sulfides to sulfoxides and converts sulfoxides to sulfones (eq 25). The partial oxidation of sulfides to sulfoxides can be controlled by limiting the quantity of DDO. Since Oxone is one of the many reagents that can perform these reactions, the extra effort involved in preparing DDO solutions is often not warranted. An exception involves the transformation of thiophenes to the corresponding sulfones (eq 26). A similar procedure gives a-0x0 sulfones by DDO oxidation of thiol esters (eq 21)P... 

Olefination of the aldehyde of 196 installed an additional carbon necessary for advancement to the natural products, giving methyl vinyl ether 197. Treatment with dimethyldioxirane at low tenperature acconplished oxidation at sulfur in the presence of the electron-rich vinyl ether, and the resulting sulfoxides (mixture of diastereomers at sulfur) underwent high-yielding Mislow-Evans rearrangement to allylic alcohol 198 under mild conditions in methanol containing trimethylphosphite and di-zso-propyl amine. The product 198 of this sequential Claisen/Mislow-Evans process was converted to either (-)-joubertinamine or (-)-mesembrine in a short series of steps. 

Figure 2 Examples of structures ftom MC simulations of reactions in solution. Only key solvent molecules from the first solvation shell are illustrated, (a) Transition structure (TS) for the Claisen rearrangement of chorismate in water, (b) TS for the epoxidation of cw-2-butene by dimethyldioxirane in methanol, (c) TS for the Mislow-Evans rearrangement of allyl p-tolyl sulfoxide in methanol, (d) Solvation of a pentamethylcyclohexyl cation in THF...

Sulfoxides are formed by oxidation using MCPBA or dimethyldioxirane [60]. 

With these modifications disaccharide A-B, then trisaccharide A-B-C could be obtained in 82 and 68% yields respectively. Oxidation of trisaccharide A-B-C with 2,2-dimethyldioxirane gave a sulfoxide (90%) which was coupled to the aglycone of ciclamycin 0 under the modified conditions in 75% yield (Figure 10). After removal of the p-methoxybenzyl ethers with DDQ the ciclamycin 0 was obtained in a 17% overall yield and with only six steps from the starting monomers. 

---