Quaternary chiral β(2,2)-amino acids with pyridinium and imidazolium substituents.
The reactions of cyclic sulfamidates as electrophiles with a variety of nitrogen-containing aromatic heterocycle nucleophiles, such as pyridines, N-alkylimidazoles and N-methylbenzimidazol, was explored. In all cases, although the nucleophilic substitution reactions occurred on quaternary centres, elimination products were not detected. The inversion of configuration at this quaternary centre was determined by X-ray diffraction analysis and the enantiomeric excess of the reactions was checked by chiral HPLC. This synthetic approach allowed us to obtain a new family of chiral charged β(2,2)-amino acids, including a new bisamino acid that incorporates an imidazolium salt as a cross-linker. In this context, the treatment of these chiral imidazolium salts with Ag(2)O opens the way to new chiral N-heterocyclic carbenes, which are important substrates in the fields of organometallic and organocatalytic chemistry. Additionally, we have done a thorough conformational analysis of these β-amino acid derivatives, both in the solid state and in solution. The most important conformational feature of these acyclic systems is the rigidity of the N-CH(2)-C-N(+) dihedral angle, which is essentially due to the gauche effect.
Departamento de Química, Universidad de La Rioja, Centro de Investigación en Síntesis Química, Logroño, Spain.
Lara
L
Mata
Alberto
A
Avenoza
Jesús H
JH
Busto
Francisco
F
Corzana
Jesús M
JM
Peregrina
D000596:Amino Acids / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007093:Imidazoles / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D011726:Pyridinium Compounds / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D014961:X-Ray Diffraction
D000596:Amino Acids; D007093:Imidazoles; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds