Regioselective Domino Synthesis of 2-Alkylflavans via Hidden Brønsted Acid CatalysisSupported by: This study was supported by the Kyung Hee University Research Fund (KHU-20130575)
Received: 25 January 2017
Accepted after revision: 24 March 2017
25 April 2017 (eFirst)
A range of alkyl-substituted flavans, which are important structural elements in natural products and pharmaceutical molecules, were prepared by successive hidden Brønsted acid catalyzed domino reaction, intermolecular hydroarylation, and intramolecular hydroalkoxylation. 1,1-Disubstituted allenes were activated under mild acidic AgOTf/t-BuCl condition to initiate the regioselective Friedel–Crafts reaction with phenol derivatives, and the consecutive reaction triggered by the 6-endocyclization led to the formation of a new type of 2-alkylflavan. Mechanistic study of the reaction intermediates and control experiments support the catalytic pathway and advantage of hidden Brønsted acid catalysis.