Highly regioselective ring opening of quinolinic[2,3]anhydrides under mild conditions

Controlled Pyrazole-Hydrazone Annulation: Regiodivergent Synthesis of 1H- and 2H-Pyrazolo[3,4-d]pyridazinones

An efficient and controlled site-selective annulation of 3,5-diethoxycarbonyl 4-hydrazonyl pyrazoles is described. The relative proportion of the products is affected by hydrazone intermediate configuration, reaction temperature, and Lewis acid employed. At a temperature of 110-120 °C, the reaction preferentially afforded 1H-pyrazolo[3,4-d]pyridazin-7(6H)-ones, whereas using Yb(OTf)₃ in MeCN reflux, 2H-pyrazolo[3,4-d]pyridazin-7(6H)-ones were favored. Computational investigations were performed to clarify the mechanism and the origin of the regiodivergence.

Crystal structure of N-[2-(cyclo-hexyl-sulfan-yl)eth-yl]quinolinic acid imide

The title compound, C15H18N2O2S {systematic name: 6-[2-(cyclo-hexyl-sulfan-yl)eth-yl]-5H-pyrrolo-[3,4-b]pyridine-5,7(6H)-dione}, was obtained from the reaction of pyridine-2,3-di-carb-oxy-lic anhydride (synonym: quinolinic anhydride) with 2-(cyclo-hexyl-sulfan-yl)ethyl-amine. The dihedral angle between the mean plane of the cyclo-hexyl ring and the quinolinic acid imide ring is 25.43 (11)°. In the crystal, each mol-ecule forms two C-H⋯O hydrogen bonds and one weak C-O⋯π [O⋯ring centroid = 3.255 (2) Å] inter-action with neighbouring mol-ecules to generate a ladder structure along the b-axis direction. The ladders are linked by weak C-O⋯π [O⋯ring centroid = 3.330 (2) Å] inter-actions, resulting in sheets extending parallel to the ab plane. The mol-ecular structure is broadly consistent with theoretical calculations performed by density functional theory (DFT).