Hydroxymethylthiamine, phosphate free "active formaldehyde, " was synthesized by the acid treatment of 2-phenyloxalylthiamine-O, O'-diacetate or 2-α-furyloxalylthiamine-O, O'-diacetate, and on alkaline treatment it was converted into a dimeric 1, 4-oxazine derivative (X) involving a ring expansion and auto-oxidation.
