Rossella Mello

Silver-Catalyzed C-C Bond Formation Between Methane and Ethyl Diazoacetate in Supercritical CO2

Supercritical carbon dioxide solvent facilitates transformation of the generally inert carbon-hydrogen bonds in methane. Even in the context of hydrocarbons’ general resistance to selective functionalization, methane’s volatility and strong bonds pose a particular challenge. We report here that silver complexes bearing perfluorinated indazolylborate ligands catalyze the reaction of methane (CH4) with ethyl diazoacetate (N2CHCO2Et) to yield ethyl propionate (CH3CH2CO2Et). The use of supercritical carbon dioxide (scCO2) as the solvent is key to the reaction’s success. Although the catalyst is only sparingly soluble in CH4/CO2 mixtures, optimized conditions presently result in a 19% yield of ethyl propionate (based on starting quantity of the diazoester) at 40°C over 14 hours.

Oxidations by methyl(trifluoromethyl)dioxirane. 3. Selective polyoxyfunctionalization of adamantane

Adamantane (1) can be converted directly into adamantan-1,3,5-triol (5) and into adamantan-1,3,5,7-tetraol (6) under remarkably mild conditions by employing an excess of isolated methyl(trifluoromethyl)dioxirane (3a) in solution. This new dioxirane species was found to be over 7,000-fold more reactive than dimethyldioxirane (3b) in performing adamantane hydroxylations.

Oxidation of acetals, an orthoester, and ethers by dioxiranes through α-CH insertion

Abstract Dimethyldioxirane ( 1a ) and methyl(trifluoromethyl)dioxirane ( 1b ) efficiently afford cleavage of acetals and of ketals to carbonyl products under mild, neutral conditions. Dialkyl ethers are cleaved to alcohols, aldehydes and/or carboxylic acids, whereas reaction of dioxiranes 1a, b with medium-ring cyclic ethers transforms the latter into lactones, via the corresponding hemiacetals, with no appreciable formation of ring-opened products. The products can be accounted for on grounds of a remarkably selective O -atom insertion by the dioxirane into C-H bonds α to the ether functionality.

Oxidation of alkynes by dioxiranes

Abstract In situ generated or isolated dimethyldioxirane (1a) and methyl(trifluoromethyl)dioxirane (1b) efficiently afford oxidation of alkynes, most likely via oxirene intermediates, which rearrange into ketene or α,γ-unsaturated carbonyls, or else are further oxidized to α,β-dicarbonyls. Diphenylacetylene and phenylacetylene yield mostly ketene derived products, whereas 8-hexadecyne (an internal dialkyl alkyne) gives 9-hexadecen-8-one (both trans and cis) as the main product. Reaction of cyclodecyne (a conformationally rigid cycloalkyne) with isolated 1b affords cis-bicyclo[5.3.0]decan-2-one (15) and cis-bicyclo[4.4.0]decan-2-one (16), which derive from the oxirene by stereoselective 1.5- and 1,6-transanular insertion, respectively.

Oxidations by methyl trifluoromethyl dioxirane. Epoxidation of enol ethers

Abstract Isolated methyl trifluoromethyl dioxirane 4b has been employed to achieve the rapid, low temperature epoxidation of enol ethers, such as alkoxy(aryl)methylidene adamantanes 1a–e and methoxy(2-naphthyl)methylidene 2-bornane 1f , affording the corresponding spirooxiranes in excellent (92–97%) yields.

Oxidations by methyl(trifluoromethyl)dioxirane. 4.1 oxyfunctionalization of aromatic hydrocarbons

Abstract By using the title dioxirane ( 1a ), naphthalene ( 2 ), phenanthrene ( 3 ), and anthracene ( 4 ) have been converted into anti -naphthalene-1,2;3,4-dioxide ( 2′ ), phenonthrene-9,10-oxide ( 3′ ), and anthraquinone ( 4′ ), respectively, in high yield and under mild conditions. However, the transformation of pyrene ( 5 ) - an higher homologue of the polycyclic aromatic hydrocarbon series - into the corresponding arene oxide was found to procced much less effectively.

Oxidation of catechol and of 2,6-di-tert-butylphenol by dioxiranes

In a biomimetic transformation, the selective oxidation of catechol (2) to Z,Z-muconic acid (3) has been achieved under extremely mild conditions using methyl(trifluoromethyl)dioxirane (1b). Both dioxirane 1b and dimethyldioxirane (1a) have been applied to the oxidation of 2,6-di-tert-butylphenol (4); the product natures suggest the incursion of radical pathways.

Epoxidation of olefins with a silica-supported peracid.

Anhydrous [2-percarboxyethyl] functionalized silica (2a) is an advantageous oxidant for performing the epoxidation of olefins 1. Epoxides 3 do not undergo the ring-opening reactions catalyzed by the acidic silica surface, except for particularly activated cases such as styrene oxide. The hydrophilic and acidic character of the silica surface does not interfere with the directing effects exerted by allylic H-bond acceptor substituents. The alkenes 1 carrying hydroxyl groups react with silica-supported peracid 2a faster than unsubstituted alkenes, thus reversing the trend known for reactions with soluble peracids. These results are attributed to the H-bond interactions of substrate 1 with the silanol and carboxylic acid groups bonded to the silica surface.

Baeyer–Villiger oxidation of ketones with a silica-supported peracid in supercritical carbon dioxide under flow conditions

[2-Percarboxyethyl]-functionalized silica reacts with ketones in supercritical carbon dioxide at 250 bar and 40 °C under flow conditions to yield the corresponding esters and lactones. The solid reagent can be easily recycled through treatment with 70% hydrogen peroxide in the presence of an acid at 0 °C. This procedure not only simplifies the isolation of the reaction products, but has the advantage of using only water and carbon dioxide as solvents under mild conditions.

One electron transfer chain decomposition of trifluoroacetone diperoxide: The first 1,2,4,5-tetroxane with O-transfer capability

Abstract Reaction of 1,1,1-trifluoropropanone (trifluoroacetone) ( 1a ) with 30% hydrogen peroxide in the presence of conc. sulfuric acid afforded in good yield 3,6-bis(trifluoromethyl)-3,6-dimethyl-1,2,4,5-tetroxane or trifluoroacetone diperoxide ( 2a ). Peroxide 2a is quantitatively converted into trifluoroacetone ( 1a ) and dioxygen by a catalytic amount of tetrabutylammonium iodide through a reductive electron transfer chain reaction carried out by the superoxide ion. Trifluoroacetone diperoxide ( 2a ) is capable of O-atom transfer to alkenes and sulfides.