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 α,β-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.

Diastereoselective construction of trans-fused octalone framework via ruthenium-porphyrin-catalyzed cycloaddition.

Lewis acid catalyzed cycloaddition of cyclohexenone and butadiene affords trans-fused octalone with high regio- and diastereoselectivity. The use of the ruthenium porphyrin complex as the Lewis acid catalyst is key to the reaction. The cycloaddition proceeds in toluene with 1 mol % of the ruthenium catalyst at 25 °C.