Salvatore Failla

Conformational investigation of N-aralkylpyridinium ions by Cotton-Mouten effect method

Abstract Molar Cotton-Mouton constants and refractions are reported at 298 K for the following N -aralkylpyridinium cations as solutes in water or acetonitrile: (C 6 H 5 )CH 2 ( + NC 5 H 5 ), (4-ClC 6 H 4 )CH 2 ( + NC 5 H 5 ), (3-ClC 6 H 4 )CH 2 ( + NC 5 H 5 ), 3-ClC 6 H 4 )CH 2 (2′-Me + NC 5 H 4 ), (4-NO 2 C 6 H 4 )CH 2 ( + NC 5 H 5 ), (2,5-Me 2 C 6 H 3 )CH 2 ( + NC 5 H 5 ), (2,5-Me 2 C 6 H 3 )CH 2 (2′-Me + NC 5 H 4 ), (2,4,6-Me 3 C 6 H 2 )CH 2 ( + NC 5 H 5 ), (2,3,5,6-Me 4 C 6 H)CH 2 ( + NC 5 H 5 ), (2,3,5,6-Me 4 C 6 H)CH 2 (2′-Me + NC 5 H 4 ), (2,3,4,5,6-Me 5 C 6 )CH 2 ( + NC 5 H 5 ) and (2,3,4,5,6-Me 5 C 6 )CH 2 (2′-Me + NC 5 H 4 ). The data are analysed in terms of the preferred conformations adopted by such cations in formations, where both aryl and pyridinium rings are twisted in the same direction with respect to the C ar -CH 2 -N ar reference plane. In contrast, tri-ortho-substituted diaryl cations adopt an asymmetric form in which the ortho-substituted aromatic ring lies almost perpendicular to the reference plane, and the mono-ortho-pyridinium ring forms an acute angle with the reference plane.

Supramolecular aggregation/deaggregation in amphiphilic dipolar Schiff-base zinc(II) complexes.

The synthesis, characterization, optical, and fluorescent properties of an amphiphilic Schiff-base bis(salicylaldiminato)zinc(II) complex are reported. Detailed (1)H nuclear magnetic resonance (NMR), diffusion-ordered spectroscopy (DOSY) NMR, optical absorption, and fluorescence spectroscopy studies indicate the existence of aggregate species in noncoordinating solvents. The degree and type of aggregation are related to the concentration and the polarity of the noncoordinating solvent. Dilute solutions are likely characterized by the presence of defined dimers, whereas larger oligomeric aggregates are conceivably formed at higher concentrations. The concentration needed to observe the formation of larger species depends upon solvent polarity. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of the system occurs, because of the axial coordination to the Zn(II) ion, accompanied by considerable changes of (1)H NMR and optical absorption spectra. A dramatic enhancement of fluorescence emission is observed in dichloromethane solutions upon deaggregation with a coordinating agent. The formation of a defined 2:1 supramolecular structure is demonstrated in the case of a ditopic ligand as coordinating species. Overall, these complexes are promising systems for the development of new supramolecular architectures and supramolecular fluorescent probes.

Facile separation of the enantiomers of diethyl N-(aryl)-1-amino-1-arylmethanephosphonates on a rationally designed chiral stationary phase

Separation of the enantiomers of each member of a series of diethyl N-(aryl)-1-amino-1-arylmethanephosphonates is easily accomplished by HPLC using a WHELK-O column. This totally synthetic chiral stationary phase (CSP 1) is designed to utilize specifiable interactions to differentiate between enantiomers. The structural features of these phosphonates suggested that CSP 1 would be applicable to the separation of the enantiomers of this class of compounds even though there was an element of uncertainty owing to the presence of two π-basic interaction sites, one on either side of the stereogenic center. The structures of the π-basic N-aryl and C-aryl substituents have been varied, the structure of the latter being found to have the greatest effect on retention and enantioselectivity.

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.

SYNTHESIS, NMR INVESTIGATION AND FAB-MS CHARACTERIZATION OF 1-AMINO-2-ARYLMETHYL-DIPHOSPHONATE ESTERS

Abstract Variously substituted amino aryl-methyl-diphosphonate ethyl esters have been prepared in good yields by adding diethyl phosphonate to the corresponding Schiff bases. All compounds were characterized by NMR and MS-FAB techniques, which reveal the presence of peaks or fragmentation patterns very useful and diagnostic for constitutional assignment. Evidences for a stereospecific addition of diethyl phosphonate to the two—CH·N—sites in diaryl diimines have been observed. The presence of heteroaromatic rings such as pyridine or azo-groups renders such compounds also very attractive for complexation studies towards metals; thus, these molecules are for potential uses in agrochemistry and biodiagnostic medicine.

SYNTHESIS OF NEW ORTHO-HYDROXY ARYL PHOSPHONATE MONOMERS

Commercially available bridged bis-phenols react with diethylphosphite to give bis-phosphates, which are easily transformed by LDA, in good yields, to bis-ortho hydroxy aryl phosphonates. These new monomers are of great relevance for the synthesis of novel macrocycles and for thermal resistant polycondensates containing phosphonate moieties.

Direct chiral HPLC separation of the enantiomers of fluorinated N-arylamino-1-arylmethylphosphonate esters. Substituent effects on the enantioselectivity

Abstract Racemic N-arylamino-1-arylmethylphosphonic acid diethyl esters with various fluorinated substituents in one or both aryl rings have been resolved in their enantiomers by a direct HPLC method, using chiral stationary phases. The chiral separation on Chiralcel OD strongly depends on the substitution pattern in the N-aryl and/or in the C-aryl moieties and it improves markedly with the polarity of the fhiorinated substitnent. A new Pirkles chiral stationary phase (R)-α-Burke 1 is more efficient and in some cases more enantioselective than other Pirkles phases. A chiral recognition model between this phase and the enantiomers of an analyte afforded to propose the absolute configuration of the optical isomers and to relate it to the chiroptical behaviour.

SYNTHESIS, NMR CHARACTERIZATION AND FAB-MS SPECTRA OF SOME ARYLMETHYL-AMINO-PHOSPHONIC ACID MONOETHYL ESTERS

Abstract Substituted arylmethyl-amino-phosphonic acid monoethyl esters have been synthetized by alkaline hydrolysis of the parent diester derivatives. Diastereoisomerizations due to racemization at the chiral ─CH─ centers were observed in the hydrolytic process. Our compounds are very soluble in water and strong polar organic solvents; therefore, these derivatives can be used for biological and agrochemical tests in hydrophilic media. Some of the prepared compounds are deeply coloured and their absorption maxima are pH-dependent. The 1H and 31P-NMR spectra show interesting features, whereas the MSFAB obtained with negative ion source are diagnostic for structural assignments. In all MS spectra, peaks due to cluster ions [nM ‐ Na]− where observed.

New molecular architectures by aggregation of tailored zinc(II) Schiff-base complexes

This contribution reports the synthesis, characterization, 1H NMR, optical absorption and fluorescence properties of a bis(salicylaldiminato)Zinc(II) Schiff base complex, 1, having dipodal, alkyl ammonium bromide derivatized side chains in the salicylidene rings. The comparison of 1H NMR and optical spectroscopic properties of 1 with those of the closely related amphiphilic alkyl derivative allowed getting insights into the nature of species in solutions. Present data suggest the existence of Zn⋯Br interactions, thus avoiding intermolecular Zn⋯O interactions, as usually occur in the absence of other coordinating species. SEM images of samples obtained by drop-casting from dichloromethane solutions of 1 reveal the existence of branched nanostructures, consistent with intermolecular Zn⋯Br interactions. The present approach thus suggests a new method to unique supramolecular architectures for coordination metal complexes.

A new facile synthesis of α-dicarbonyl compounds by oxidation of alkynes with Mo(VI) peroxocomplex promoted by mercuric acetate

Abstract Mercuric acetate promoted oxidation of diaryl-, dialkyl-, and aralkyl alkynes with (HMPA)MoO(O2)2 in 1,2-dichloroethane affords the corresponding α-diketones in good yields. Likewise, terminal alkynes can be converted into α-ketoaldehydes in excellent yields by using the same oxidizing system.