Crystal structure of 1-ethyl-3-(2-oxo-1,3-di-thiol-4-yl)quinoxalin-2(1 H)-one

The title compound I, C₁₃H₁₀N₂O₂S₂, crystallizes in the monoclinic space group C2/c with eight mol-ecules in the unit cell. Excluding for the ethyl substituent, the mol-ecule of I adopts a nearly coplanar conformation (r.m.s. deviations is 0.058 Å), which is supported by the intra-molecular C-H⋯O hydrogen-bonding inter-action between the two ring systems [C⋯O = 2.859 (3) Å]. In the crystal, the mol-ecules form dimeric associates via two bifurcated C-H⋯O hydrogen-bonding inter-actions between an ene hydrogen atom and a carbonyl functional group of an adjacent mol-ecule [C⋯O = 3.133 (3) Å] and vice versa. The crystal structure is further stabilized by a three-dimensional network of weak hydrogen bonds between one mol-ecule and six adjacent mol-ecules as well as offset π-π stacking. The combination of the quinoxaline 2(1H)-one moiety with the di-thio-carbonate moiety extends the aromaticity of the quinoxaline scaffold towards the substituent as well as influencing the π-system of the quinoxaline. The title compound is the direct precursor for a di-thiol-ene ligand mimicking the natural cofactor ligand molybdopterin.