Oxygen insertion reagents

Dioxiranes in general and DMD in particular are very efficient as oxygen insertion reagents at carbon centers, and are often capable of effecting transformations under mild conditions that... 

How does oxygen insert in between the B—bonds Let s take a closer look at the reagents— a hydroxide ion can deprotonate hydrogen peroxide to form a hydroperoxide anion ... 

In this instance, the first-formed alkyl bis(phenylthio)antimony derivative is very air sensitive, and undergoes oxygen insertion into the carbon-antimony bond. The resultant peroxy intermediate then rearranges rapidly to the pentavalent derivative, from which the alcohol can be released on hydrolysis. The specific example shown below in Scheme 17 is indicative of the power of this transformation, although it must be admitted that the method requires very pure, thiophenol-free antimony reagent. 

A theoretical study on the oxidation of methane, propane and isobutane with dioxirane, dimethyldioxirane, difluorodioxirane and methyl(trifluoromethyl)di-oxirane has provided a rational for the formation of radical intermediales when dioxygen is rigorously excluded and supported the generally accepted, highly exothermic, concerted oxygen insertion mechanism for the oxidation under typical preparative conditions. The activation barriers for the oxidation of methane (44.2), propane (30.3) and isohutane (22.4 kcal mol" ) with dimethyldioxirane have been evaluated [48e]. Perfluorodialkyloxaziridines are also mild and selective reagents for the hydroxylation of alkanes [49] ... 

The direct attack of the front-oxygen peroxo center yields the lowest activation barrier for all species considered. Due to repulsion of ethene from the complexes we failed [61] to localize intermediates with the olefin precoordinated to the metal center, proposed as a necessary first step of the epoxidation reaction via the insertion mechanism. Recently, Deubel et al. were able to find a local minimum corresponding to ethene coordinated to the complex MoO(02)2 OPH3 however, the formation of such an intermediate from isolated reagents was calculated to be endothermic [63, 64], The activation barriers for ethene insertion into an M-0 bond leading to the five-membered metallacycle intermediate are at least 5 kcal/mol higher than those of a direct front-side attack [61]. Moreover, the metallacycle intermediate leads to an aldehyde instead of an epoxide [63]. Based on these calculated data, the insertion mechanism of ethene epoxidation by d° TM peroxides can be ruled out. 

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