One-Pot Synthesis and Photochemical Diversification of Pyrazolo[1,2- a ]pyridazinones into 3D-Rich Scaffolds

We report a one-pot, three-component synthesis of pyrazolo[1,2-a]pyridazinones from tetrahydropyridazines, a transformation that was historically challenging due to competing ring contractions. The resulting compounds undergo photoinduced transformations, without the need for external photocatalysts, to afford diverse 3D-rich derivatives, including tricyclic cyclobutenes and γ-(pyrazol-1-yl)butanals. Enabled by mild conditions, this strategy offers an efficient, atom-economical route to structurally diverse pyrazolo[1,2-a]pyridazinones and their derivatives.