Lucia D'Accolti

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.

Selective oxidation of tertiary-secondary vic-diols to α-hydroxy ketones by dioxiranes

Abstract Isolated dimethyldioxirane ( 1a ) and methyl(trifluoromethyl)dioxirane ( 1b ) efficiently afford the conversion of bicyclic diols bicyclo [2.2.2]octane-1,2-diol ( 2 ) and (+)-pinane-2,3-diol ( 6 ), of tricyclic diols adamantane-1,2-diol ( 3 ), homoadamantane-3,4-diol ( 4 ), and of homopentaprismane-3,4-diol ( 5 ) into the corresponding α-hydroxy ketones in high yields and under mild conditions. In the oxidation of (+)-pinane-2,3-diol ( 6 ), (−)-2-hydroxy-3-pinanone ( 11 ) is obtained in optical yield > 97% with retention of configuration.

Photoreduction of Carbon Dioxide to Formic Acid in Aqueous Suspension: A Comparison between Phthalocyanine/TiO2 and Porphyrin/TiO2 Catalysed Processes

Composite materials prepared by loading polycrystalline TiO2 powders with lipophilic highly branched Cu(II)- and metal-free phthalocyanines or porphyrins, which have been used in the past as photocatalysts for photodegradative processes, have been successfully tested for the efficient photoreduction of carbon dioxide in aqueous suspension affording significant amounts of formic acid. The results indicated that the presence of the sensitizers is beneficial for the photoactivity, confirming the important role of Cu(II) co-ordinated in the middle of the macrocycles. A comparison between Cu(II) phthalocyanines and Cu(II) porphyrins indicated that the Cu(II)- phthalocyanine sensitizer was more efficient in the photoreduction of CO2 to formic acid, probably due to its favorable reduction potential.

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.

Selective oxidation of O-isopropylidene derivatives of diols to 2-hydroxy ketones employing dioxiranes☆

Employing dimethyldioxirane (1a) or methyl(trifluoromethyl)dioxirane (1b), the direct conversion of O-isopropylidene derivatives of 1,2-diols into the corresponding 2-hydroxy ketones can be achieved in high yield and under mild conditions; optically active acetonides are transformed into homochiral 2-hydroxy ketones in high optical yield, and with preservation of configuration at the C∗OH chiral center proximal to that undergoing oxidation to carbonyl. The diacetonide of 1,4-Diphenylbutan-1,2:3,4-tetraol could be selectively converted into 1,4-diphenyl-1-oxo-2-hydroxy 3,4-acetonide, with removal of just one acetonide moiety.

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.

Concerning Synthesis of Ring-A Fluorinated Anthracyclines. The Dioxirane Shunt

Abstract In a key step of the synthesis of 8-fluoro anthracycline aglycones such as 7, epoxidation of the electron-poor C8–C9 double bond moiety presented by the 8-acetyl-6,11-dimethoxy-7,10-dihydronaphthacene-5,12-dione starting material can be achieved in high yield and ease of operations using methyl(trifluoromethyl)dioxirane (1b). †Dedicated to Prof. W. Adam (University of Würzburg) on the occasion of his 65th birthday.

On the hydroxylation of bicyclo[2.1.0]pentane using dioxiranes

Abstract The oxidation of bicyclo[2.1.0]pentane by isolated dimethyldioxirane and by the more powerful methyl(trifluoromethyl)dioxirane, affords selectively, the corresponding endo -2 alcohol along with the 2,3-diol in high yield, and no rearrangement products; this suggests that a concerted O -insertion mechanism should be preferred over radical pathways.

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.