Abstract The photochemical behaviour of some substituted aldehyde thiosemicarbazones 1a-k has been investigated in methanol at 254 nm. Thiosemicarbazones of glyoxil methyl ester 1a-f cyclized to furnish the 3-thioxo-1, 2, 4-triazin-5-one 2 ring system. The remaining thiosemicarbazones 1g-j gave 1, 2, 4-triazoline 4 derivatives.
