Regioselectivity dioxiranes

Aryl-l,2,4,5-tetrazines are oxidised by methyl(trifluoromethyl)dioxirane to their previously unknown iV-oxides 96. NMR studies have shown that N-l is oxidised regioselectively <96X2377 >. 

In addition to metal catalyzed oxygenation of nonactivated alkane C-H bonds, oxofunctionalization of C-H bonds can also occur in water by using dioxiranes.20 Alkylketones and alkylketoesters could be regioselectively oxidized at the 5-position of the aliphatic chain by dioxiranes generated in situ by oxone in a mixture of H20/MeCN... 

Recently, substantial progress has been registered in regard to the regioselective CH oxidations by dioxiranes. Usually, the regioselectivity of the CH oxidation is mainly governed by the reactivity of the C—H bond for example, in the above-mentioned oxidation of c -decalin , the tertiary C—H bond is selectively oxidized in the presence of the secondary C—H bonds. When the reactivities are similar, the regioselectivity is determined by steric factors. For example, the preferential oxyfunctionalization of the tertiary C—H bond at the C-14 position of the steroid 19 by DMD in the presence of the other tertiary C—H bonds at the C-5, C-8 and C-9 positions is due to steric reasons (equation 30) . ... 

A novel approach to achieve high regioselectivity was recently developed by Yang and coworkers, in which the in-situ-generated dioxirane functionality, contained within the substrate, oxidizes the secondary 5c-h bond rather than the more reactive tertiary yc-H bond, due to a favorable concerted transition state (equation 31). A limitation of this method, however, is that the ketone unit has to be incorporated into the substrate molecule at the appropriate position, normally a rather unpractical and cumbersome task. Moreover, such a process is necessarily stoichiometric in practice and, thereby, it lacks appeal since nowadays catalytic enantioselective oxyfunctionalizations are in vogue ... 

Two new reactive, very powerful organic peroxides, dimethyldioxirane and methyl(trifluoromethyl)dioxirane (4), have been introduced.81-83 The latter is more reactive and can be used more conveniently.84 85 Acyclic alkanes give a mixture of isomeric ketones on oxidation with methyl(trifluoromethyl)dioxirane,84,85 while cyclohexanone is the sole product in the oxidation of cyclohexane (99% selectivity at 98% conversion).85 With the exception of norbomane, which undergoes oxidation at the secondary C-2 position, highly selective tertiary hydroxylations can be carried out with regioselectivities in the same order of magnitude as in oxidations by peracids.85-87 A similar mild and selective tertiary hydroxylation by perfluorodialkyloxaziridines was also reported.88 Oxidation with dioxiranes is highly stereoselective 85... 

The chemoselectivity, regioselectivity, diastereoselectivity, and enantioselectivity of heteroatom oxidations, epoxidations and CH insertions by dioxiranes have been reviewed.26 The selective ring-opening reactions of epoxides at high pressures have been reviewed (in Japanese).27... 

Regioselective oxidation of trifluoromethyl ketones (via dioxiranes) occurs at the unactivated 8-carbon atom. ... 

The N(l) atom of 3-aryl-l,2,4,5-tetrazines is oxidized regioselectively by methyl(trifluoro-methyl)dioxirane to give the hitherto unknown iV(l)-oxides (96T2377). 

Horiguchi T, Nagura M, Cheng Q, Oritani T, Kudo T (2000) Chemical Oxidation of Taxoids with m-CPBA and Dimethyl Dioxirane Regioselective Epoxidation of Taxinine J Derivatives. Heterocycles 53 2629... 

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