posted on 2021-07-02, 08:14authored byJuan F. Tamez-Fernández, Fátima M. Soto-Suárez, Yolanda D. Estrada-Chavarría, Ramiro F. Quijano-Quiñones, Rubén A. Toscano, Fabián Cuétara-Guadarrama, Víctor Duarte-Alaniz, Tannya R. Ibarra-Rivera, Beatriz Quiroz-García, Diego Martínez-Otero, Karla Ramírez-Gualito, José Enrique Barquera-Lozada, Verónica M. Rivas-Galindo, Gabriel Cuevas
The
cyclopropane ring-opening reaction of riolozatrione, a natural
product obtained from Jatropha dioica, afforded a 2,2-disubstituted 1,3-cyclohexandione displaying an
alkyl methyl ether group at position 5. The conformational analysis
of this product showed a high preference for the trans-diaxial conformation in both solution and solid state. Such conformation
was possible from the noncovalent intramolecular nX →
π*CO interactions (X = an element having
an unshared electron pair), allowing the determination of the interaction
energies. Since the nX → π*CO interactions can be regarded as additive, the energy values ranged
from 4.52 to 6.51 kcal mol–1 for each carbonyl group
with a strong dependency on the interatomic distances. The rigorous
analysis of the electron density in the topological theory of atoms
in molecules framework clearly shows that the origin of O–CO
interactions are through the nO → π*CO electron transfer mechanism. Such interactions are slightly weaker
than a canonical hydrogen bond but seemingly stronger than a van der
Waals interaction. This interaction must be considered as a stereoelectronic
effect due the electronic transfer between the interacting groups,
which are limited by their relative stereochemistry and can be represented
by a bond–no bond interaction, causing the pyramidalization
of the carbonyl, which is the charge acceptor group.