Hydroxyl Assisted, Photoredox/Cobalt Co-catalyzed Semi-Hydrogenation and Tandem Cyclization of o-Alkynylphenols for Access to 2,3-Dihydrobenzofurans

Herein, a hydroxyl assisted, photoredox/cobalt co-catalyzed semi-hydrogenation and tandem cyclization of o-alkynylphenols is developed towards direct assembly of 2,3-dihydrobenzofurans. Moderate to good yields were obtained for a range of sterically and electronically diverse 2-propynolphenols under mild conditions. Mechanistic studies demonstrated the inevitable role of the alcoholic hydroxyl group with (Z)-alkene as the real intermediate. Finally, a key low-valent cobalt catalyzed intramolecular hydroetherification of alkene is proposed.

Automated summary

A novel hydroxyl assisted, photoredox/cobalt co-catalyzed semi-hydrogenation and tandem cyclization reaction has been developed for the direct assembly of 2,3-dihydrobenzofurans, with moderate to good yields obtained for a variety of 2-propynolphenols under mild conditions. Mechanistic studies revealed the essential role of the alcoholic hydroxyl group and proposed a key low-valent cobalt catalyzed intramolecular hydroetherification of alkene.