Michele Fiorentino

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.

Enantioselective epoxidation of unfunctionalized alkenes using dioxiranes generated in situ

Abstract Using (+)-3-(trifluoroacetyl)camphor, or R (+)- and S (−)-3-methoxy-3-phenyl-4,4,4-trifluoro-butan-2-one as precursors for chiral dioxiranes generated in situ , the asymmetric epoxidation of prochiral alkenes trans - β -methylstyrene, trans -2-octene, and cis -2-methyl-7-octadecene has been achieved in 12–20% ee.

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. 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.

High-yield synthesis of nitriles by oxidation of aldehyde N,N-dimethylhydrazones with dimethyldioxirane☆

Abstract Using dimethyldioxirane, the selective transformation of aldehyde N , N -dimethyl-hydrazones into the corresponding nitriles was achieved in high yield and under mild conditions. The detemination of the substituent effect on rates, along with an estimate of the primary kinetic isotope effect using PhCHNNMe 2 and PhCDNNMe 2 provided useful hints concerning the reaction mechanism. It was also observed that the nitrile products do not undergo further oxidation, even with excess dioxirane.

CHEMO- AND DIASTEREOSELECTIVITIES IN THE OXIDATION OF CYCLOPENTENOLS WITH DIMETHYLDIOXIRANE AND METHYL(TRIFLUOROMETHYL)DIOXIRANE

Abstract A comparison of the diastereoselectivity and the chemoselectivity (epoxidation versus allylic oxidation) attained in the oxidation of cyclopentenols using dimethyldioxirane and methyl(trifluoromethyl)dioxirane is reported. The results indicate that with both dioxiranes diastereoselective epoxidation of allylic cyclopentenols is accompanied by competitive allylic oxidation to the corresponding enone; for the latter, a likely rationale is proposed.

Asymmetric epoxidation of unfunctionalized alkenes by dioxirane intermediates generated from potassium peroxomonosulphate and chiral ketones

Chiral dioxirane intermediates, which are formed in the reaction of potassium peroxomonosulphate with chiral ketones, allow the epoxidation of simple pro-chiral olefins to the corresponding epoxides to be carried out with enantiomeric excesses in the range 9–12.5%.

Structural effects on the reactivity of carbon radicals in homolytic aromatic substitution. Part 4. The nucleophilicity of bridgehead radicals

The reactions of 1-adamantyl (1), 3,3-dimethylbicyclo[2.2.2]octan-1-yl (2), and 7,7-dimethylbicyclo[2.2.1]heptan-1-yl (3) radicals with protonated pyridines and quinoline have been investigated and the relative rates of substitution have been determined. The results obtained showed that the three bridgehead radicals have nucleophilic properties which decrease in the order: (1) > (2) > (3). This behaviour is explained on the basis of a different degree of charge development in the transition state of the addition step of the radicals to the protonated substrates, as a consequence of different ring strain in the three polycyclic systems. A comparison of the present results with those already available for other alkyl radicals is also reported, in order to evaluate the effect of electronic configuration on the reactivity of carbon radicals in homolytic aromatic substitution.

m-Chloroperbenzoic acid oxidation of dioxins and dihydrodioxins

The m-chloroperbenzoic acid (MCPBA) oxidation of dihydrodioxins affords, in high yield, ethylene glycol dibenzoates, via unstable epoxy diethers. These elusive intermediates have been characterized chemically and by 1H n.m.r. spectroscopy. In contrast, the MCPBA oxidation of 2,3,5,6-tetraphenyl-p-dioxin fails to give the corresponding (Z)-stilbenediol dibenzoate but yields instead benzil