Imidazole and benzimidazole addition to quinones. Formation of meso and d,l isomers and crystal structure of the d,l isomer of 2,3-Bis(benzimidazol-1'-yl)-1,4-dihydroxybenzene

Abstract

The hydroquinones obtained by addition of imidazole, 2-methylimidazole and benzimidazole to 1,4-benzoquinone and 1,4-naphthoquinone have been isolated and identified. In the case of 1,4-benzoquinone they are monosubstituted hydroquinones 1a - 1e, o-substituted hydroquinones 2a - 2c, and p-disubstituted derivatives 3a - 3c while in the case of 1,4-naphthoquinone, only disubstituted derivatives 5a and 5c have been isolated. In solution, 2,3-bis(2′-methylimidazol-1′-yl)-1,4-dydroxybenzone ( 2b), 2,3-bis (benzimidazol-1′-yl)-1,4-dihydroxybenzene ( 2c) and 2,3-bis(benzimidazol-1′-yl)-1,4-dihydroxynaphthalene ( 5c) exist as mixtures of meso and d,l isomers. NMR spectroscopy (n.O.e. experiments in 1H NMR and solid-state 13C CPMAS spectra) and AM1 semiempirical calculations have been used to establish the structure of the isomers both in the solid state and in solution as well as their interconversion pathways. Compound 2c- d,l crystallizes with two methanol solvate molecules as guests and it has a crystallographic twofold axis through the middle. The host molecules are linked together by means of the methanol molecules through O-H⋯O/N hydrogen bonds giving rise to chains along the c axis centrosymmetrically related.