Luis Muñoz

Determination of the absolute stereochemistry of Etzionin

Abstract The absolute configuration of Etzionin, a marine peptide-like compound isolated in 1989 from a red tunicate collected from the Red Sea has been determined by a combination of synthetic and spectroscopic procedures. Finally, its absolute stereochemistry has been established as 3 S ,3′ R .

Convenient Synthesis of Oxazolidinones and Oxazinones from Allyl and Homoallyl Amines under Mild Conditions

Abstract An efficient one‐pot general method for the high‐yield synthesis in solution of oxazolidinones and oxazinones from allyl‐ and homoallylamines, respectively, has been developed. The reaction is carried out at an atmospheric pressure between 0°C and room temperature using a solution of carbon dioxide in acetonitrile and hindered guanidine as the base.

Chemistry of amidines. Part 1. Determination of the site of initial protonation in N′-pyridylformamidines

A series of substituted N,N-dimethyl-N′-pyridylformamidines has been synthesised and the pKa values of the conjugate acids have been measured in water at 25 °C. Consideration of the pka values shows that initial protonation is predominantly on the imino nitrogen of the amidine system rather than on the pyridyl nitrogen. The effect of the protonation on the 1H and 13C NMR spectra of the amidines is discussed.

Asymmetric synthesis of the β-amino acid methyl ester derivative of onchidin: (2S,3S)-methyl-3-amino-2-methyl-7-octynoate and its enantiomer

Abstract The asymmetric synthesis of the methyl ester of the natural β-amino acid of Onchidin (2 S ,3 S )-methyl-3-amino-2-methyl-7-octynoate and its enantiomer is described. The preparation of an enantiomerically pure β-hydroxy acid through an enantioselective aldol condensation reaction and an intramolecular nucleophilic displacement to form a β-lactam intermediate are the key steps.

Chemistry of amidines. Part 2. Substituent and solvent effects on rotational barriers in N′-pyridylformamidines

Values of ΔG‡ for rotation about the carbon–dimethylamino bond in a range of substituted pyridyl formamidines have been determined by 1H NMR spectroscopy in a small range of solvents. The correlation of ΔG‡ with σ– is interpreted in terms of a coplanar amidine and pyridine system. The variation of ΔG‡ with solvent is interpreted in terms of hydrogen bonding to the amino lone pair of the amidine.

Structural and conformational study of (±) (6 S , 7 R )-3-aza-7-iodo-1-oxaspiro[5.5]undecan-2-one

Abstract The single crystal X-ray structure of racemic (6 S , 7 R )-3-aza-7-iodo-1-oxaspiro[5.5]undecan-2-one 1 shows, in the solid state, a cyclohexane ring in a chair conformation with the iodine and the oxygen substituents in axial positions. The oxazinone ring presents a sofa like conformation (conformation 1). Theoretical and experimental conformational analyses also reveal the presence in solution of, at least, two more conformations: one with the inverted chair in the cyclohexane (conformation 3) and the other with the inverted sofa in the oxazinone (conformation 2).

Chemistry of amidines. Part 3. Analysis of conformation about the N′-pyridyl bond in N′-(2-pyridyl)formamidines

A conformational analysis of a series of N,N-dimethyl-N′-(2-pyridyl)formamidines and their conjugate acids using the 1H NMR nuclear Overhauser effect shows that they exist preferentially in the conformation in which the pyridine and the imino nitrogen lone pairs are anti. For compounds having electron-donating substituents the syn conformation becomes important on protonation.

Chemistry of amidines. Part 4. Analysis of conformation for a series of N′-pyridylformamidines by 1H NMR spectroscopic, molecular mechanical and semi-empirical molecular orbital methods

The results of NOE measurements for a series of N′-pyridylformamidines and their conjugate acids have been interpreted with the aid of molecular mechanical and semi-empirical molecular orbital calculations. Conformations about the pyridyl–Nim and the Cf–Nam bonds are determined by delocalisation of the Nam lone pair, dipolar interactions, steric interactions and, in the conjugate acids, long range interaction between the pyridyl N and the electron-deficient formyl H.