Enantio- and Diastereoselective Synthesis of Substituted Tetrahydro-1H-isochromanes through a Dynamic Kinetic Resolution Proceeding under Dienamine Catalysis

Racemic 5-acyloxydihydropyranones react with enolizable α,β-unsaturated aldehydes in the presence of a chiral secondary amine catalyst furnishing a wide range of differently substituted tetrahydro-1H-isochromanes with excellent results. The reaction relies on the activation of the enal by the catalyst through the formation of a dienamine intermediate, which undergoes a Diels–Alder/elimination cascade reaction. Moreover, the overall transformation also results in a highly efficient dynamic kinetic resolution process, furnishing the final adducts in high yields and excellent diastereo- and enantioselectivities.