rac-(2R,3S)-2-Phenyl-3-(3-phenyl-1,2,3,4-tetrahydroquinoxalin-2-yl)quinoxaline

Abstract

The title compound, C28H22N4, is the unexpected by-product of the reaction of 2-hydroxyacetophenone and 1,2-diaminobenzene under iodine catalysis, during which a carbon–carbon σ-bond between two quinoxaline units was formed. Although a fully oxidized title compound should sterically be possible, only one quinoxaline ring is fully oxidized while the second ring remains in the reduced form. As expected, the tetrahydroquinoxaline unit is not planar; it adopts a sofa conformation, whereby the atom joining the two heterocyclic systems lies out of the plane of the other atoms. The quinoxaline ring system makes a dihedral angle of 53.61 (4)° with its phenyl ring substituent. The crystal packing is determined by pairs of N—H...N, N—H...π and weak C—H...N hydrogen bonds, forming a chain parallel to the a axis.