Publication Date: 2016.
The crystal structures of nine compounds (1-9) bearing the 4-aminofuran-2(5H)-one scaffold (commonly known as tetronamide, C4H5NO2) and two decorating aromatic/heteroaromatic moieties with two stereocenters have been determined. Tetronamides bearing at the 5-position a phenyl moiety (1 and 2, 3-chloro derivatives with either a 4-p-tolylamino or 4-p-bromophenylamino substituent), an o-bromopyridyl moiety (3, a 3-bromo-4-p-tolylamino derivative), or an o-tolyl moiety (4, a 3-bromo-4-p-tolylamino derivative) adopt a U-shaped conformation. This conformation is stabilized by an intramolecular contact involving either the phenyl o-CH moiety (1 and 2) or the substituent at the ortho position (3 and 4) and the π system of the N-phenyl ring. The other five tetronamides (5-9) are not present with such an intramolecular contact. In fact, these last five compounds are not U-shaped and feature the presence at the 5-position of a p-biphenyl moiety (5 and 7, 3-bromo-4-p-tolylamino diastereomers differing as 5R and 5S), a p-methoxyphenyl moiety (6, a 3-chloro-4-p-bromophenylamino derivative), or a 5-chlorofuran-2-yl moiety (8 and 9, 3-chloro-4-p-tolylamino diastereomers differing as 5R and 5S). Crystal structures of a 5,5-disubstituted tetronamide bearing m-nitrophenyl moieties (10) and a parent tetronamide without a substituent at the 5-position (11d) reinforce the conformational trend found in 1-9. Furthermore, OH···O centrosymmetric dimers are formed only in the crystal structures of the U-shaped tetronamides. Chain motifs assembled through OH···O and NH···O hydrogen bonds are preferred in the line-shaped tetronamides. Furthermore, the conformer energies were calculated in both the gas and solution phases (B3LYP/6-31G∗). The lowest-energy conformations feature an intramolecular N-H···O hydrogen bond as in the crystal structure of 7. In the U-shaped tetronamides, the crystal structure conformations are similar to the third or fourth energetically ranked stable calculated conformer. Therefore, it is concluded that the substitution pattern in the U-shaped tetronamides allows for accessible secondary minimum-energy conformations that are easily adopted in the crystal structure as a result of their compatibility with the robust centrosymmetric O-H···O dimer formation.
Author affiliation: Karak, Milandip. Universidade Federal de Minas Gerais; Brasil. Universidade Federal de Viçosa; Brasil
Author affiliation: Acosta, Jaime A. M.. Universidade Federal de Minas Gerais; Brasil
Author affiliation: Barbosa, Luiz C. A.. Universidade Federal de Minas Gerais; Brasil. Universidade Federal de Viçosa; Brasil
Author affiliation: Sarotti, Ariel Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina
Author affiliation: Da Silva, Cameron C.. Universidade Federal de Goiás; Brasil
Author affiliation: Boukouvalas, John. Universite Laval; Francia
Author affiliation: Martins, Felipe T.. Universidade Federal de Goiás; Brasil
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas