/sci/ - Science & Math

What's the mechanism here?
I assume that 2 sulphur gets 2 protons and 2 electrons from a CH3-CH2 couple, forming a 1,3 diene. At this point, there is an attack by other 2 atoms of sulphur, forming a bis-thioketone, which then gives the thiophene through a Paal-Knorr like reaction.