Quaternary Chiral β2,2‐Amino Acids with Pyridinium and Imidazolium Substituents |
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Authors: | Lara Mata Prof Alberto Avenoza Dr Jesús H Busto Dr Francisco Corzana Prof Jesús M Peregrina |
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Institution: | Departamento de Química, Universidad de La Rioja, Centro de Investigación en Síntesis Química, Madre de Dios, 51. 26006 Logro?o (Spain), Fax: (+34)?941299620 |
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Abstract: | 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 β2,2‐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 Ag2O 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‐CH2‐C‐N+ dihedral angle, which is essentially due to the gauche effect. |
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Keywords: | amino acids conformational analysis heterocycles imidazoles molecular dynamics nucleophilic substitution |
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