Ruthenium-Porphyrin-Catalyzed [4+2] Cycloaddition of α,β-Unsaturated Imines and Aldehydes

A new efficient synthetic route to unsymmetrically substituted dihydropyridine scaffolds via dehydrative [4+2] cycloaddition of N-tosylated alpha,beta-unsaturated imines with aldehydes has been developed. This transformation is enabled by (i) the remarkable catalytic ability of the cationic Ru(IV) porphyrin complex to activate both the imino and carbonyl groups and (ii) the hydrophobic nature of the porphyrin ligand, which helps realize robust Lewis acidity in the dehydrative cycloaddition.