Enantioselective Intermolecular Mannich-Type Interception of Phenolic Oxonium Ylide for the Direct Assembly of Chiral 2,2-Disubstituted Dihydrobenzofurans

An enantioselective intermolecular Mannich-type interception of phenolic oxonium ylides with imines has been developed. The cooperative catalysis with achiral dirhodium complex and chiral phosphoric acid has been introduced to circumvent the competitive phenolic O–H bond insertion via dual H-bonding, enabling the synthesis of enantioenriched 2,2-disubstituted dihydrobenzofurans with good to high yield and high to excellent enantioselectivity under mild conditions. Preliminary antitumor activity study of these generated products indicated that the reduction product 7 exhibits high anticancer potency against human lung adenocarcinoma cells (A549 cells, IC50 = 9.13 μM).