Synthesis of Pyridazines by a Diels-Alder Strategy

Significance

The synthesis of substituted pyridazines by Diels-Alder reaction of unsymmetrical 1,2,4,5-tetrazines with various dienophiles in moderate to high yields is reported. The electron-deficient tetrazines allow the use of mild conditions in reactions with a wider range of electron-rich dienophiles including ketene acetals, enol ethers, enamines and enamides. The cycloadditions proceed regioselectively as confirmed by X-ray crystal structure analysis for four of the adducts.