Brønsted Acid Catalyzed Friedel–Crafts Alkylation of Naphthols with In Situ Generated Naphthol-Derived <i>ortho</i>-Quinone Methides: Synthesis of Chiral and Achiral Xanthene Derivatives
Sushree Ranjan Sahoo, Vinod K. Singh
Abstract
We disclose herein an enantioselective protocol for the Brønsted acid catalyzed addition of naphthols to in situ generated naphthol-derived ortho -quinone methides ( o -QMs) followed by intramolecular cyclization, which delivers substituted chiral xanthene derivatives, in a one-pot reaction sequence under mild conditions. This process serves to convert naphthol-derived ortho -hydroxyl benzylic alcohols into reactive naphthol-derived o -QMs using a chiral phosphoric acid (CPA) catalyst. Moreover, it is helpful in controlling the enantioselectivity of the carbon–carbon bond-forming event via hydrogen-bonding followed by intramolecular cyclization. Additionally, for the first time, we observe a Brønsted acid catalyzed C(sp 2 )–C(sp 3 ) bond cleavage of naphthol-derived ortho -hydroxyl benzylic alcohols for the synthesis of achiral xanthene (sigma plane containing) derivatives in good to excellent yields.