3,5,6-Trimethyl-thieno[2,3-d]pyrimidin-4(3H)-one.

In the title compound, C(9)H(10)N(2)OS, the thienopyrimidine ring system is almost planar [greatest deviation from the mean plane = 0.0318†(13)†à for the S atom]. The crystal packing features C-H⋯O hydrogen bonds and π-π stacking inter-actions between inversion-related pairs of mol-ecules with a centroid-centroid distance of 3.530†(3)†à .