Advances in the synthesis of functionalized tetrahydropyridazines from hydrazones

The tetrahydropyridazine motif is widely present in plenty of natural products and biologically active molecules. Easily prepared from the condensation of carbonyls with hydrazines, hydrazones are versatile synthetic building blocks that are frequently used in organic synthesis. Hydrazones are also utilized in the synthesis of nitrogen-containing molecules, especially nitrogen-containing heterocycles. The presence of the CN–N unit in the product makes hydrazones ideal substrates for the synthesis of tetrahydropyridazine derivatives. Here, in this review, we summarize the recent progress in the construction of variously substituted tetrahydropyridazines from different hydrazone derivatives together with mechanism discussions.