S. Nakai, M. Yasui, M. Nakazato
Dec 15, 2003
Citations
0
Influential Citations
15
Citations
Journal
Bulletin of the Chemical Society of Japan
Abstract
The fundamental physical properties of 2-methyl and 2-phenylimidazo[1,2-a]pyrazin-3(7H)-one 1 and 2, and their N- and O-alkylated derivatives 3–6 have been investigated by X-ray crystallography, UV/vis absorption spectroscopy, NMR, and AM1-COSMO calculations. The crystal structures of 3 and 4 showed that the imidazo[1,2-a]pyrazin-3(7H)-one (imidazopyrazinone) π-system has a planar ring structure and a weakened carbonyl character of the C3–O10 bond, suggesting that the imidazopyrazinone π-system has the character of a zwitter-ionic resonance structure to increase the aromaticity. The data concerning the bond length alternations and the NMR chemical shifts of 1–4 also support that their imidazopyrazinone rings have small portions of aromatic character. In addition, imidazopyrazinone derivatives 1–4 showed solvatochromism originating by hydrogen-bonding interactions with hydrogen-bond donor solvent molecules; derivatives 1 and 2 prefer to be the NH form isomers in their tautomeric equilibriums. These observa...