Fabio Ponticelli

Synthesis of functionalized quinolines and benzo[c][2,7]naphthyridines based on a photo-Fries rearrangement.

An efficient one-pot method for the synthesis of functionalized quinolines and tetrahydronaphthyridines has been developed. The photo-Fries rearrangement of p-substituted anilides afforded differently substituted o-amino ketones that reacted in situ with acetylenic Michael acceptors such as dimethyl acetylenedicarboxylate (DMAD) to give 6,4-disubstituted quinoline 2,3-dicarboxylates. Starting from anilides derived from β-alanine, a naphthyridine nucleus can also be assembled.

Synthesis and antiperoxidant activity of new phenolic O-glycosides.

We describe the synthesis of some 3-tert-butyl-4-hydroxyphenyl D-glycopyranosides by reaction of tert-butylhydroquinone with beta-D-pentaacetyl-glucose, beta-D-pentaacetyl-galactose, 2-acetamido- and 3,4,6-tri-O-acetyl-2-butanamido-2-deoxy-beta-D-glucopyranosyl chlorides as well as the formation of anomeric 3-tert-butyl-4-hydroxyphenyl 4,6-di-O-acetyl-2,3-dideoxy-D-erythro-hex-2-eno-pyranosides by reaction between tert-butylhydroquinone and 3,4,6-tri-O-acetyl-D-glucal. All compounds, except 3-tert-butyl-4-hydroxyphenyl alpha- and beta-D-glucopyranosides, inhibited lipid peroxidation with a degree of potency comparable to that of tert-butyl hydroxyanisole.

CHARACTERIZATION AND DIFFERENTIATION OF HETEROCYCLIC ISOMERS. TANDEM MASS SPECTROMETRY AND MOLECULAR ORBITAL CALCULATIONS ON 3-METHYLISOXAZOLO- AND 2- METHYLOXAZOLOPYRIDINES

Metastable mass-analyzed ion kinetic energy (MIKE) and collision-induced dissociation MIKE spectrometries have been applied to the study of all members of two classes of heteroaromatic isomers: 3-methylisoxazolo-and 2-methyloxazolopyridines. The study revealed that tandem mass spectrometry can characterize and differentiate the isomeric ion structures produced by these heterocycles. In particular, the MIKE spectra of both the molecular ions and abundant fragments formed by CO and CH3CN losses show characteristic differences that allow distinction among the isomers dependent on the position of the nitrogen atom in the pyridine ring, and distinction of isoxazole derivatives from oxazoles. The results indicate that the isomerization of the isoxazole moiety to oxazole-proposed for other analogous compounds—does not occur in these heterocyclic systems. The experimental work is supported by molecular orbital calculations both on neutral molecules and on molecular and fragment ions.

Trapping of photochemical intermediates as a tool in organic synthesis. Preparation of spiroaziridinopyridones, a new heterocyclic system

Whereas alkyl lithium and Grignard reagents both at rt and at −80°C thermally react with 3-methylisoxazolo[5,4-b]pyridine giving alkylation and/or isoxazole ring opening products, sodium malonate and sodium boron hydride react only under UV irradiation. Selective trappings of ketenimine or azirine intermediates give an enaminopyridone or two diasteroisomeric spiroaziridinopirydones. Regioselective opening of the aziridine ring with perchloric acid gives 3(1-amino-ethyl)-1H-pyridin-2-one.

Synthetic Approach, Regio- and Stereochemical Characterization and Differentiation of New Potential Antioxidant C- And O-Arylglycosides

Two series of C- and O-arylglycosides with potential antioxidant properties have been synthesized, characterized and structurally differentiated. Reinvestigation of a synthetic approach has provided better insight into the products obtained and their chemical structures. Regio- and stereochemical characterization and differentiation of each compound have been carried out in solution, in the crystal, and in the gas phase. A comparison between the data obtained in solution and the crystal structures suggests closely related features in the two states. Mass spectrometry proved very effective for characterization of and differentiation between C- and O-isomers, as well as positional isomers. Unimolecular reactions occurring in the gas phase are specific to the chemical structures, and ion abundances can be related to their stabilities. This study has allowed the evaluation of the influences of the different linkages between the two moieties and the positions of the substituents on the chemical properties of the compounds. The C-isomers show antioxidant capability, as peroxyl radical scavengers, and inhibit lipid peroxidation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Carbon‐13 NMR studies on azolopyridines 2—The oxazolopyridine systems

The 13C NMR spectra of oxazolopyridine systems are discussed, and a simple method for distinguishing between 2‐methyloxazolo‐ and 3‐methylisoxazolo‐pyridines is suggested, based on the chemical shift of the methyl group. The effect of the 2‐methyloxazole fusion on the pyridine ring is comparable to that of 3‐methylisoxazole, judging by 1J(CH) values determined from line splittings.

Synthesis, structural and conformational properties, and gas phase reactivity of 1,4-dihydropyridine ester and ketone derivatives

A new series of 4-aryl-2,6-dimethyl-1,4-dihydropyridines, characterized by ester or ketone functions at positions 3 and 5, has been synthesized. Structural and conformational properties, concerning the dihydropyridine ring and the orientation (synplanar/antiperiplanar) of the substituents have been investigated in their crystal structure and in solution by nuclear magnetic resonance. Evaluation of intermolecular and hydrogen bonding interactions as well as packing features, have been also carried out, evidencing interesting packing motifs. Their gas phase reactivity, as protonated and deprotonated molecules, has been investigated by electrospray ionization, high resolution and collision-induced dissociation multiple stage mass spectrometry. Deydrogenation reactions have been observed as a function of the capillary voltage.

Photocycloadditions on 2-Methyloxazolo[5,4-b]pyridine

The title compound undergoes photocycloadditions with both electron-poor alkenes (methacrylonitrile) and electron-rich alkenes (ethyl vinyl ether and furan). The initial photoadducts evolve into a variety of compounds. In the photoreaction with methacrylonitrile, oxazoloazocines 5 and 7 and cyclopentenylidenes 6Z and 6E are obtained; the photoadducts with vinyl ether yield oxazoloazocines 9 and 11, substituted oxazoles 10 and 12, and pyrrolopyridine 13; from the reaction with furan the furylpyridine 14 was isolated. (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2002)

A New One Step Synthetic Approach to the Isoxazolo[4,5-b]Pyridine System

Abstract A convenient direct entry to the title ring system by condensation-cyclization processes of 3,5-dimethyl-4-nitroisoxazole (1) with the enamines 2 and 8 is reported; some reactions of the resulting N-oxides 5 and 10 are also described.

Photodimerization of N-benzyl-1,4-dihydronicotinamide

Abstract N-benzyl-1,4-dihydronicotinamide dimerized on irradiation with λ=365nm across 2,3 and 5,6 double bonds to give the product I which closed to centro-symmetric cage dimer IV on further irradiation with λ⩽313nm.