Total synthesis of rac-sumatranin C and 8-epi-sumatranin C via a Ni-promoted reductive cyclization and tandem coupling

Sumatranin C possesses a unique 2,3,3a,9a-tetrahydro-4H-furo[2,3- b ]chromene heterotricyclic framework and three contiguous stereocenters, and presents good selectivity indexes against LPS-induced B lymphocyte proliferation. Herein, we report the total synthesis of sumatranin C and its 8-epimer via a nickel-promoted reductive cyclization of β-bromo acetal and tandem coupling with aryl iodide, which led to an efficient construction of the unique skeleton embedded in this furopyran lignan.