Abstract magnified image In an attempt to carry out a straightforward synthesis of thiazolopyrazolodiazepines from the reaction of 4,5‐diamino‐3‐methyl‐1‐phenylpyrazole 1 with arylidene derivatives of rhodanine 2 , the unplanned (Z) ‐ 2′‐[(5‐amino‐3‐methyl‐1‐phenylpyrazol‐4‐yl)imino]‐5‐arylidenethiazolidin‐4‐ones 4 were obtained as unique products. Nevertheless, the treatment of these compounds with aliphatic aldehydes in dimethylformamide provided the novel thiazolo[2,3‐ b ]pyrazolo[3,4‐ f ][1,3,5]triazepines 5 and 6 in good to excellent yields. All the structures of the obtained compounds were assigned on the basis of IR, 1D and 2D NMR measurements, mass spectrometry, and microanalysis. J. Heterocyclic Chem., (2009).