Sulfides reaction with oxaziridines

Asymmetric sulfide oxidations are reported using oxaziridines other than A -sulfonyloxaziridines, but it is necessary to use a protic acid or Lewis acid to increase their reactivity. For example, -tolyl methyl sulfide 152 with bicyclic oxaziridine 153 in the presence of TFA gave the (A)-sulfoxide 154 in 50% yield and 42% ee in 24 h <1999T155>. It is interesting to note that use of MsOH resulted in much faster reaction with the oxidation complete in less than a minute. Similarly, sulfide 155 with chiral oxaziridine 156 in the presence of zinc chloride afforded sulfoxide 157 in 30% yield and 55% ee <2005JOC301>. 

Sulfoxide linkers can be synthesized via addition of a sulfoxide linker to the resin or via transformation of a sulfide linker to the corresponding oxo-derivative. Many oxidation reagents like ozone or mCPBA to convert thioethers are very unselective regarding sulfoxide/sulfone formation but methodologies like acid-catalyzed oxaziridine oxygen transfer [298], H2O2/HFIP oxidation [299] or reaction with a fBuOOH/CSA-mixture [300] can be applied successfully. 

The formal addition of an oxygen atom across the carbonyl group gives rise to dioxiranes (equation 33). In practice, this reaction is effected with Oxone, and dimethyldioxirane (30) and other dioxiranes have been generated in solutions of their parent ketones.Dioxirane (30) has been implicated in oxidations of alkenes, sulfides and iinines. The formal addition of nitrogen across a carbon-oxygen double bond to afford oxaziridines has been reviewed (equation 34).There are also many methods available for the indirect conversion of carbonyl compounds to aziridines > and thiiranes using multi-step conversions. 

The mechanism of oxygen transfer from oxaziridines to nucleophiles is believed to involve an Sn2 type reaction and this assumption is supported by theoretical and experimental studies. When sulfides are oxidized to the corresponding sulfoxides and sulfones, the molecular recognition is steric in origin, and it is determined by the substituents on both the substrate and the oxaziridine. For the oxidation of enolates, the molecular recognition is explained with an Sn2 mechanism as well as by an open (non-chelated) transition state where the nonbonded interactions are minimized. The mechanism of oxygen transfer to an enolate to form the corresponding acyloin is shown below. ... 

The treatment of simple and fused oxaziridines with sulfur-containing nucleophiles such as thiourea, potassium thiocyanate, potassium ethyl-xanthate, potassium selenocyanate, and triphenyl-phosphine sulfide resulted in the formation of the related imines, most probably—in analogy to the results of the treatment of oxiranes with the same reagents—via the corresponding thiaziridine intermediate. The proposed reaction mechanism is given in Scheme 8 <73AJC2159>. 

Variously substituted phosphorus(V) sulfides and selenides were converted to the corresponding oxides by fiuorooxaziridines. For example, reaction of triisobutylpho-sphine sulfide (314) with oxaziridine 294 in dichloropentafluoropropane gave the oxide 315 in 92% yield, together with elemental sulfur. Surprisingly, it was found with a chiral sulfide that the reaction occurred with clean inversion of configuration, whereas retention was observed when the oxidant was MCPBA. 

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