Maurizio D'Auria

Oxidative ring opening of furan derivatives to α,β-unsaturated γ-dicarbonyl compounds, useful intermediates for 3-oxocyclopentenes synthesis

Abstract α,β-unsaturated γ-dicarbonyl compounds, easily obtained by reaction of pyridinium chlorochromate with alkylfurans, are interesting starting materials for the rapid synthesis of 3-oxo-cyclopentenes.

SINGLET OXYGEN IN THE PHOTODEGRADATION OF LIGNIN MODELS

Abstract The photochemical oxidation of lignin models in the presence of singlet oxygen was studied. The treatment of the non-phenolic β-O-4 aryl ether derivatives 6 , 7 , and 8 in the presence of both oxygen and Rose Bengal gave products deriving from a formal β-C-O cleavage formation. By this way, the derivatives 12 , 13 , and 15 were obtained. The photochemical oxidation of the phenolic β-O-4 aryl ehter 9 gave the same type of product confirming that, in this case, the presence of the carbonyl group is not indispensable to have the cleavage reaction. The use of the model compound 10 showed that, when the phenoxy part of the molecule shows a lower reactivity towards singlet oxygen, the oxidation of the phenol moiety to hydroquinone can occur. The photochemical behaviour of these model compounds can be rationalised from a reaction of singlet oxygen with the phenoxy part of the molecule.

A new synthesis of 3-oxocyclopentenes

Abstract 5 - Methyl - 2 - furylcarbinols 3 have been converted into 3-oxocyclopentene derivatives 4 through a molecular rearrangement catalyzed by ZnCl 2 . The reaction mechanism is explained in terms of a thermal electrocyclic reaction of a 4π electrons system. An application relative to the synthesis of (±) allethrolone is reported. reported.

Photodegradation of lignin : the role of singlet oxygen

The photochemical irradiation of some phenoxyacetophenone derivatives in the presence of oxygen by using visible light did not produce any decomposition product. In the presence of singlet oxygen, sensitized by using Bengal Rose, decomposition products were obtained. The products obtained were similar to those obtained by direct β-C-O cleavage on the substrate. In this case, the observed behavior can be explained assuming an attack of singlet oxygen on a phenoxy part of the molecule.

Singlet oxygen degradation of lignin

Abstract Lignin obtained by steam explosion of straw, beech (a hardwood plant), and pine (a softwood plant) was isolated and characterized by using standard methods. The irradiation of lignins with visible light in the presence of oxygen and of a singlet oxygen sensitizer (Rose Bengal) induced several modifications in the lignin structures that were monitored by using gel permeation chromatography (GPC) and UV spectroscopy. We observed a remarkable reduction of the mass distribution by GPC when monitoring at 280 nm and the shift of the residual chromatograms to mass values lower than the native lignins. These data are in agreement with a depolymerization reaction of lignins. The UV spectra showed that all the chemical species of lignins undergo several modifications during the irradiation reaction. Thus, the E 1 band reduced its absorbance and underwent a hypsochromic shift. The E 2 , and the B band were greatly reduced during the irradiation.

Photochemical dimerization of esters of urocanic acid

Abstract The irradiation of urocanate esters in the presence of benzophenone in acetonitrile with a mercury lamp led to the formation of dimers. Methyl and ethyl urocanate gave a 2:1 mixture of dimethyl or diethyl c-3,t-4-di(1H-imidazol-4-yl)cyclobutane-r-l,t-2-dicarboxylate and dimethyl or diethyl t-3,c-4-di-(1H-imidazol-4-yl)cyclobutane-r-1,t-2-dicarboxylate. The allyl urocanate gave in high yields only of diallyl c-3,t-4-di(1H-imidazol-4-yl)cyclobutane-r-1,t-2-dicarboxylate. The regiochemistry of the reaction can be explained considering the frontier orbital interactions. The stereochemistry of the reaction can be justified on the basis of the ΔHf of the products. In all the cases, the most stable dimers were obtained.

Photochemical synthesis of diindolylmethanes

Abstract The photochemical reaction of an aromatic aldehyde with indole or 2-methylindole gave 3,3′-diindolylmethanes in ca. 50% yield. A mechanism involving a electron transfer process is proposed.

Oxetane Synthesis through the Paternò-Büchi Reaction

The Paternò-Büchi reaction is a photochemical reaction between a carbonyl compound and an alkene to give the corresponding oxetane. In this review the mechanism of the reaction is discussed. On this basis the described use in the reaction with electron rich alkenes (enolethers, enol esters, enol silyl ethers, enanines, heterocyclic compounds has been reported. The stereochemical behavior of the reaction is particularly stressed. We pointed out the reported applications of this reaction to the synthesis of naturally occuring compounds.

The Paternò-Büchi Reaction of 2-Furylmethanols

The Paterno-Buchi reaction between 2-furylmethanol derivatives and aromatic carbonyl compounds shows good regioselectivity and high stereoselectivity. The regio- and stereoselectivity of the reaction can be explained by assuming a role of both the substituent on the 2-furylmethanol derivative and the hydroxy group in order to favor the approach of the carbonyl group towards a prochiral face of the furan. Electrochemical and kinetic properties of 2-furylmethanols are in agreement with an electron-transfer mechanism. The stereoselectivity of the reaction was confirmed using chiral 2-furylmethanols: These substrates gave the corresponding Paterno-Buchi adducts with high enantiomeric excess.

General route and mechanism of the rearrangement of the 4-substituted 5-hydroxy-3-oxocyclopentenes into the 2-substituted analogs

Abstract A general method of synthesis of hydroxycyclopentenones of type 6 starting from the isomeric compound 2 is described. This conversion is shown to occur through an alumina-catalyzed process of intramolecular hydration.