Organocatalytic Asymmetric Friedel−Crafts Alkylation/Cyclization Cascade Reaction of 1-Naphthols and α,β-Unsaturated Aldehydes: An Enantioselective Synthesis of Chromanes and Dihydrobenzopyranes

An enantioselective Friedel−Crafts alkylation/cyclization cascade reaction of 1-naphthols and α,β-unsaturated aldehydes promoted by diphenylprolinol ether has been developed. The method affords one-pot access to chiral and synthetically useful chromanes and dihydrobenzopyranes in high yields and enantioselectivities from readily available compounds. In addition, the addition/cyclization products could be afterward transformed to various natural products and biologically active derivatives. On the basis of the experimental results and the observed absolute configurations of the products, a plausible mechanism has been proposed to explain the origin of the activation and the asymmetric induction.