Selective synthesis of hydroxy analogues of valinomycin using dioxiranes.

A synthesis of representative monohydroxy derivatives of valinomycin (VLM) was achieved under mild conditions by direct hydroxylation at the side chains of the macrocyclic substrate using dioxiranes. Results demonstrate that the powerful methyl(trifluoromethyl)dioxirane 1b should be the reagent of choice to carry out these key transformations. Thus, a mixture of compounds derived from the direct dioxirane attack at the β-(CH(3))(2)C-H alkyl chain of one Hyi residue (compound 3a) or of one Val moiety (compounds 3b and 3c) could be obtained.

Selective hydroxylation of methane by dioxiranes under mild conditions.

The direct conversion of methane to methanol at low temperatures was achieved selectively using dioxiranes 1a,b either in the isolated form or generated in situ from aqueous potassium caroate and the parent ketone at a pH close to neutrality. Results suggest that the more powerful dioxirane TFDO (1b) should be the oxidant of choice.

Concerning selectivity in the oxidation of peptides by dioxiranes. Further insight into the effect of carbamate protecting groups.

With use of methyl(trifluoromethyl)dioxirane (TFDO), the oxidation of some tripeptide esters protected at the N-terminus with carbamate or amide groups could be achieved efficiently under mild conditions with no loss of configuration at the chiral centers. Expanding on preliminary investigations, it is found that, while peptides protected with amide groups (PG = Ac-, Tfa-, Piv-) undergo exclusive hydroxylation at the side chain, their analogues bearing a carbamate group (PG = Cbz-, Moc-, Boc-, TcBoc-) give competitive and/or concurrent hydroxylation at the terminal N-H moiety. Valuable nitro derivatives are also formed as a result of oxidative deprotection of the carbamate group with excess dioxirane.

Oxyfunctionalization of non-natural targets by dioxiranes. 6. On the selective hydroxylation of cubane.

By using methyl(trifluoromethyl)dioxirane (TFDO), the direct mono- and bishydroxylation of cubane could be achieved in high yield under remarkably mild conditions. Comparison of the rates of dioxirane O-insertion with those of standard reference compounds, such as adamantane and cyclopropane, as well as ab initio computations provide useful hints concerning the mechanism of these transformations.

Concerning the reactivity of dioxiranes. Observations from experiments and theory.

The challenging hypothesis of a "biphilic" (i.e., electrophilic vs nucleophilic) character for dioxirane reactivity, which envisages that electron-poor alkenes are attacked by dioxiranes in a nucleophilic fashion, could not be sustained experimentally.

A novel approach to the efficient oxygenation of hydrocarbons under mild conditions. Superior oxo transfer selectivity using dioxiranes.

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.

Practical applications of the Fenton reaction to the removal of chlorinated aromatic pollutants. Oxidative degradation of 2,4-dichlorophenol.

Background: Chlorophenols (CPs) constitute a group of organic pollutants that are introduced into the environment as a result of several man-made activities, such as uncontrolled use of pesticides and herbicides, and as byproducts in the paper pulp bleaching. Promising removal technologies of chlorinated aromatics consist in the application of advanced oxidation processes (AOPs) that can provide an almost total degradation of a variety of contaminants. Among these, wide application find Fenton systems based on generation of reactive species having a high oxidizing power, such as hydroxyl radical HO*.

Oxyfunctionalization of non-natural targets by dioxiranes. 5. Selective oxidation of hydrocarbons bearing cyclopropyl moieties.

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.

Oxyfunctionalization of Non-Natural Targets by Dioxiranes. 3.(1) Efficient Oxidation of Buckminsterfullerene C(60) with Methyl(trifluoromethyl)dioxirane.

By employing methyl(trifluoromethyl)dioxirane (1b), the stepwise oxyfunctionalization of C(60) can be carried out with high conversions (>90%) under mild conditions (0 degrees C); the products have been compared with those produced by the oxidation of C(60) with m-chloroperoxybenzoic acid. Along with the previously characterized oxide C(60)O, a wider set of higher oxidation products is obtained by using 1b; among these, regioisomeric dioxides C(60)O(2) are isolated in good overall yield (40%). One of the dioxides is predominant (yield 23%), corresponding to a C(s)()-symmetry dioxide previously well characterized and presenting the epoxide functionalities in close proximity over the 6:6 ring junctions.