Conformational studies of N-carbomethoxy-2-alkoxyindolenines by dynamic NMR, crystallography, and molecular mechanics
2005; Elsevier BV; Volume: 61; Issue: 37 Linguagem: Inglês
10.1016/j.tet.2005.07.023
ISSN1464-5416
AutoresOscar R. Suárez‐Castillo, Yaneth M. A. Contreras-Martínez, L. Beiza-Granados, M. Melendez‐Rodriguez, José Roberto Villagómez‐Ibarra, J. Martín Torres‐Valencia, Martha S. Morales‐Ríos, Pedro Joseph‐Nathan,
Tópico(s)Crystal structures of chemical compounds
ResumoThe synthesis of N-carbomethoxy-2-alkoxyindolenines and the transformation to their tautomeric indoles is reported. Variable-temperature 1H NMR studies of these 2-alkoxyindolenines evidenced dynamic processes involving two low-energy E and Z equilibrating conformers around the N–C(O) carbamate bond, for which the barriers (ΔG≠) between the two conformations are in the order of 12.5–13.9 kcal/mol, as deduced from computational NMR line shape simulations. The rotational barrier decreases as the bulkiness of the alkoxyl group increases, with the E conformer being always more stable. Molecular mechanics calculations evidenced a preferred quasi-axial position of the alkoxyl group in the five-membered ring as the steric effect increases, in agreement with X-ray diffraction studies.
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