Derivatives of benzo[b]furan. Part I. Conformational studies of khellinone and visnaginone

• Published in: Structural chemistry 2012-10, Vol.23 (5), p.1573-1584
• Main Authors: Pena Ruiz, Tomas, Drzewiecka, Aleksandra, Koziol, Anna E., Fernandez Gomez, Manuel, Ostrowska, Kinga, Struga, Marta, Kossakowski, Jerzy
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Computer Applications in Chemistry; Original Research; Physical Chemistry; Theoretical and Computational Chemistry
• ISSN: 1040-0400; 1572-9001
• DOI: 10.1007/s11224-012-9959-4

The structural analysis of khellinone and visnaginone indicated the planarity of the benzo[b]furan ring system. The oxygen or carbon atoms of the substituents, – O H, – O CH 3 , and – C (=O)CH 3 , are nearly coplanar with the aromatic ring. The molecular conformation is stabilized by the intramolecular O–H···O hydrogen bond formed between the ortho -substituted hydroxyl and acetyl groups. The intermolecular contacts present in the crystal structure are the C–H···O and C–H···π interactions and the π··· π stacking. The energy surface for the internal rotation about the C sp2 –O/C bonds in the khellinone and visnaginone molecules has been explored by quantum-chemical calculations. The density functional theory (DFT) methods yielded three stable conformers of khellinone and two of visnaginone obtained by a rotation of the methoxy group about the C 4 sp2 – O CH 3 bond. The most stable conformation in the gas phase is consistent with the stereochemistry of the molecules adopted in the solid. The secondary minima conformers have energies higher by 0.3–1.8 kcal/mol. The energy of the intramolecular O–H···O interactions, present in the molecular structure of all stable conformers, is around 18 kcal/mol at the DFT level. A complete and reliable assignment of the bands in the IR and Raman spectra of both compounds has been performed. Graphical Abstract The distances between the C atoms (‘left’ or ‘right’ molecule) and the mean plane of the central molecule.