Investigation of Weak Noncovalent Interactions Directed by the Amino Substituent of Pyrido- and Pyrimido-[1,2-a]benzimidazole-8,9-diones

Abstract

Quinones are small redox-active molecules that are able to form intra-and intermolecular interactions both in the solid state and in solution. On the basis of 6-amino-substituted pyridoand pyrimido-[1,2-a]benzimidazole-8,9-diones, weak interactions were investigated by single-crystal X-ray and 1 H NMR spectroscopy methods. Crystallization of quinone derivatives containing a − NH−CH 2 − fragment led to the formation of both chiral and achiral crystals. The presence of two forms with (endo form) and without (exo form) an intramolecular hydrogen bond was experimentally detected by X-ray crystallography analysis and variable-temperature (VT) 1 H NMR experiments in the cases of isopentylamino-and benzylamino-substituted derivatives. Interestingly, the exo form dominates both in the solid state and in solution.

Studies of the Functionalized α-Hydroxy-p-Quinone Imine Derivatives Stabilized by Intramolecular Hydrogen Bond

“…It can be obtained in one-step synthesis from commercially available tetrachloro-1,4benzoquinone and 2-aminopyridine [17]. During earlier studies [17][18][19], it was proved that quinone 1a and some of its derivatives are electrochemically active compounds. Investigation of the reactivity of heterocyclic quinones 1 with Cand N-nucleophiles (primary amines) indicated that the attack of the nucleophile proceeds selectively at the C(6)-position of quinone.…”

“…Quinone derivatives 3a-g (Scheme 1a, atoms are numbered according to ORTEP diagram, vide infra) were obtained by the nucleophilic substitution of a chlorine atom of quinone 1a,b by benzohydrazides 2a-d. Isolated compounds 3a-g have a red-orange color in the solid state. Interestingly, in the case of aminoderivatives of quinone 1 (a merocyanine on the base of the o-quinone form), deep-blue colored crystals were obtained [17,19]. In general, derivatives containing aroyl hydrazine fragments were expected as a result of such substitution [15,20], and a few tautomeric structures can be supposed for the products [21,22].…”