Synthesis of Tetrahydropyridazine Amino Acid Derivatives by a Formal [4+2] Cycloaddition Reaction of 1,2-Diaza-1,3-dienes with Dehydroalanine Esters.

A highly efficient formal inverse electron demand aza Diels–Alder reaction of 1,2-diaza-1,3-dienes (DDs) is accomplished using dehydroalanine esters (DhAs) as electron-rich dienophiles. Both diastereoisomers of unprecedented α,α-disubstituted cyclic tetrahydropyridazine amino acids were obtained in excellent yields, in refluxing acetonitrile without activation.