Iminium Ion Catalysis: The Enantioseclective Friedel-Crafts Alkylation- Acetalization Cascade of Naphthols with α,β-Unsaturated Cyclic Ketones

The Friedel-Crafts (F-C) reaction represents one of the most powerful ways for the generation of a new C-C bond between an electron-rich aromatic system and a suitable electrophile. During the last years organocatalysis demonstrated to be a suitable strategy to realize this venerable transformation in an enantioselective fashion. Exploiting the capability of primary amine catalyst to realize unique reaction pathways with elevated enantiocontrol,4 we envisioned that a new asymmetric organocascade reaction based on a Friedel-Crafts alkylation followed by acetalization between naphthols and α,β-unsaturated ketones would be feasible. Under the optimized reaction conditions, the desired products were obtained in good yields and high enantiomeric excesses Interestingly, using indenones as electrophiles, only the F-C reaction occurs in slightly longer reaction times, but also with very good results in terms of yields and enantioselectivities.