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The design of efficient and general methods for the selective oxyfunctionalization of unactivated carbon-hydrogen bonds continues to represent a major challenge for the community of chemists, despite the fact that the oxidation of alkanes is a major feature of the chemical economy. A low level of selectivity is characteristic of large-scale oxidation of hydrocarbons performed under customary industrial oxidizing conditions (e.g., the catalytic air oxidation of cycloalkanes); in these processes, selectivity is difficult to control, because they are often impacted by the usual problems associated with free-radical chain reactions. Thus, in the last decades much work has been devoted to the search for general methods of selective oxidation that could be applied to a variety of satured hydrocarbons. In this context, just a few leading methods appear encouraging at the present time. This Account addresses a new approach developed in our laboratory, consisting in the application of isolated dioxiranes, a class of powerful yet selective oxidants. We contend that the method shows promise to contribute resolution of a well-recognized general problem in the existing chemistry of alkanes, that is, to achieve efficient oxyfunctionalizations with high selectivity for simple as well as structurally complex targets.

Abstract:The dimethyldioxirane oxida-served. Even for these alkenes, which are proposed radical mechanism. The selection of a-methylstyrene, rruns-cyclo-prone to radical reactions, the previously tive hydroxylation of ( -)-2-phenylbutane octene, and 1 -vinyl-2,2-diphenylcycloestablished electrophilic concerted mech-by dimethyldioxirane gave only ( -)-2-propane gave, under all reaction condi-anism applies, rather than the recently phenylbutan-2-01 with complete retention tions employed, the corresponding epoxof configuration and no loss of optical ides in high yields. No radical products purity. Thus, a radical-chain oxidation is also discounted in the oxygen insertion infrom allylic oxidation, from translcis isoto hydrocarbon C-H bonds for dioximerization, or from cyclopropylcarbinyl ranes. rearrangement (radical clock) were ob-

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The powerful methyl(trifluoromethyl)dioxirane (1b) was employed to achieve the direct oxyfunctionalization of 2,4-didehydroadamantane (5), spiro[cyclopropane-1,2'-adamantane] (9), spiro[2.5]octane (17), and bicyclo[6.1.0]nonane (19). The results are compared with those attained in the analogous oxidation of two alkylcyclopropanes, i.e., n-butylcyclopropane (11) and (3-methyl-butyl)-cyclopropane (14). The product distributions observed for 11 and 14 show that cyclopropyl activation of alpha-C-H bonds largely prevails when no tertiary C-H are present in the open chain in the tether; however, in the oxyfunctionalixation of 14 cyclopropyl activation competes only mildly with hydroxylation at the tertiary C-H. The application of dioxirane 1b to polycyclic alkanes possessing a sufficiently rigid framework (such as 5 and 9) demonstrates the relevance of relative orientation of the cyclopropane moiety with respect to the proximal C-H undergoing oxidation. At one extreme, as observed in the oxidation of rigid spiro compound 9, even bridgehead tertiary C-H's become deactivated by the proximal cyclopropyl moiety laying in the unfavorable "eclipsed" (perpendicular) orientation; at the other end, a cyclopropane moiety constrained in a favorable "bisected" orientation (as for didehydroadamantane 5) can activate an "alpha" methylene CH2 to compete effectively with dioxirane O-insertion into tertiary C-H bonds. Comparison with literature reports describing similar oxidations by dimethyldioxirane (1a) demonstrate that methyl(trifluoromethyl)dioxirane (1b) presents similar selectivity and remarkably superior reactivity.

Organic functionalization of carbon nanotube sidewalls is a tool of primary importance in material science and nanotechnology, equally from a fundamental and an applicative point of view. In this paper, a mild and easily tunable approach to the sidewall decoration of single-walled carbon nanotubes (SWCNTs) with epoxides and their subsequent derivatization (ring opening) upon treatment with reactive nucleophiles is presented. The treatment of HiPco purified SWCNTs with dioxirane solutions results in highly oxidized CNTs, which are used as electrophilic platforms for their successive derivatization/functionalization. As a result of the choice of accessible, easy to handle and store dioxiranes, multiple oxidation cycles could be performed on the same sample, thus allowing for a final improvement in the extent of oxidation at the CNT sidewall

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