All the possible 1‐ and 3‐monomethyl, monophenyl, dimethyl, diphenyl, and methylphenyl‐1H‐pyrazolin‐5‐ones have been condensed with o‐aminobenzaldehyde. In some cases (but not all) 1‐H‐pyrazolo[3,4‐b]quinolines (10) are formed together with a variety of other products. The balance between formation of hydrazone 11 and the ring‐closed 10 is discussed, as is the formation of other products obtained in these condensations.

2‐Amino‐benzaldehyd (I) kondensiert mit den Pyrazolinonen (II) zu den Reaktionsprodukten (III) bzw. (IV).