Manuel González-Sierra

Tautomerism of representative aromatic α-hydroxy carbaldehyde anils as studied by spectroscopic methods and AM1 calculations. Synthesis of 10-hydroxyphenanthrene-9-carbaldehyde

The synthesis of 10-hydroxyphenanthrene-9-carbaldehyde and its anil are described. The structure of the latter compound has been thoroughly studied by 1H and 13C NMR, UV-visible absorption, fluorescence and IR spectroscopies. All the experimental results support the existence of this anil mainly in the keto-enamine tautomeric form. A comparison is presented with previously studied anils derived from salicylaldehyde and 2-hydroxynaphthalene-1-carbaldehyde. Semiempirical calculations (AM1) concerning the relative stability of tautomers as well as the optimized molecular geometries are in good agreement with the experimental findings

13C NMR SPECTROSCOPIC AND AM1 STUDY OF THE INTRAMOLECULAR PROTON TRANSFER IN ANILS OF SALICYLALDEHYDE AND 2-HYDROXYNAPHTHALENE-1-CARBALDEHYDE

Tautomeric equilibria in intramolecularly hydrogen bonded Schiff bases is studied on the basis of solution 13C NMR chemical shifts. Variable temperature NMR spectroscopic data and comparison with appropriate models show that while anils of salicaldehyde exist as phenolic tautomers, those of 2-hydroxynaphthalene-1-carbaldehyde exist as equilibrium mixtures containing appreciable amounts of both enol and keto tautomers, the latter being slightly predominant. AM1 results concerning the relative stability of tautomers are in good agreement with the NMR spectroscopic information.

Iron(III) complexes of lactobionic acid : equilibrium and structural studies in aqueous solution

The equilibrium constants for the protonation of lactobionic acid (4-O-β-D-galactopyranosylgluconic acid) and its co-ordination with FeIII were studied by potentiometric methods in aqueous solution, at 20.0 °C and I= 0.100 mol dm–3(NaNO3). The equilibrium data were processed with the Fortran computer program BEST. Correlations of chelate hydrolysis constants with those of the D-gluconic acid–iron(III) system were carried out. Co-ordination bonding sites and stereochemistry of metal–ligand interactions were inferred from UV and NMR spectroscopy.

Reactivity of 1-nitronaphthalene and 1,3-dinitronaphthalene with conjugated dienes. An easy access to N-naphthylpyrroles

1-Nitronaphthalene reacts at high temperature with poor and moderately reactive dienes affording N-naphthylpyrroles while, with the same dienes, 1,3-dinitronaphthalene exhibits the dienophilic character of naphthalenic C3C4 bond producing the corresponding phenanthrenes through a classical Diels–Alder process.

Studies Toward the Total Synthesis of Saudine : Simple and Stereoselective Synthesis of a Model Caged Ketal Backbone

Abstract The synthesis of the tetracyclic mainframe containing the caged ketalic backbone of saudin was accomplished through a straight forward sequence starting from α-tetralone. The sequence included the stereoselective preparation of a key epoxy alcohol that allowed, by means of an intramolecular radical cyclisation, the total control of the relative stereochemistry of four consecutive chiral centers.

The reductive alkylation of aromatic ketones revisited. A new stereoselective route to highly functionalized 4a,8a-substituted 1,2,3,4,4a,6,8a,9,10,10a-decahydrophenanthrenes.

Abstract A series of highly functionalized angularly substituted bicyclic and tricyclic ketones were obtained regio-and stereoseltively by means of a Birch reductive alkylation.

Resolution and absolute configuration of a tricyclic lactone. A potentially useful precursor of highly functionalized terpenoids

Abstract The highly functionalized tricyclic lactone 1 was obtained in optically pure form by the sulfoximine-mediated resolution of the enone methyl acetal 3. The absolute configuration of (−)-3 and consequently of (+)-1, was determined by the transformation of (−)-3 into (−)-5, a known intermediate in the total synthesis of forskolin (2) and confirmed by application of the high field FT NMR Mosher method to alcohol 6.

Stereoselective Synthesis of (5R, 65)-(-) Erythro-6-Acetoxy-5-Dodecanolide, A Lower Homologue of a Mosquito Oviposition Attractant Pheromone, from Argentilactone

Abstract Starting from argentilactone [(5R)-(-)- δ -lactone of 5-hydroxydodeca-Z,Z-2,6-dienoic acid] and via the hydrobromic acid opening of the 65, 75-epoxide followed by acetylation and catalytic hydrogenation of the corresponding bromohydrin, (5R, 65)-(-)-erythro-6-acetoxy-5-dodecanolide was obtained. Through the 6R, 7R-epoxide and following the same sequence, the stereoisomer (5R, 6R)-(+)-threo-6-acetoxy-5-dodecanolide, was also synthesized.

Complexation of aluminium(III), gallium(III) and indium(III) ions with D-gluconic and lactobionic acids. A potentiometric and nuclear magnetic resonance spectroscopic study

The interaction of the trivalent metal ions aluminium(III), gallium(III) and indium(III) with D-gluconic and lactobionic (4-O-β-D-galactopyranosylgluconic) acids has been studied by means of potentiometry and NMR spectroscopy. Potentiometric measurements gave the stoichiometry, species distribution and equilibrium constants of the complexes in aqueous solution at 20.0 °C and /= 0.10 mol dm–3(NaNO3). The 13C NMR spectroscopic studies revealed line-broadening effects upon complexation, which selectively affected those carbons involved in the complex formation. This enabled the co-ordination sites at both acids to be elucidated. It seems that whereas aluminium(III) prefers to displace the OH protons from the sugar acids even in alkaline media, gallium(III) and indium(III) are able to form hydroxo complexes on increasing the pH.

13C NMR spectroscopic study of the tautomeric equilibrium in p-phenyl substituted benzoylacetones

Solution 13C NMR chemical shifts are reported for a series of p-phenyl substituted benzoylacetones which undergo a fast, intramolecular proton-transfer reaction between both possible enol tautomers. This information, together with 13C NMR spectroscopic data for related non-exchanging model compounds, allows the study of substituent-induced equilibrium shifts. The results show a systematic trend: electron-withdrawing para groups shift the equilibrium towards the methyl keto form.