Construction of the ABCE-ring structure of talatisamine via decarboxylative radical cyclization

Abstract Talatisamine (1) is a C19-diterpenoid alkaloid with a synthetically challenging hexacyclic ABCDEF-ring structure. Herein we report a radical-based strategy for constructing the 6/7/5/6-membered ABCE-ring 8a. After assembling the 3 known fragments, an AE-ring, an allylstannane, and a C-ring, irradiation of the ACE-ring with Hg lamp in the presence of phenanthrene and 1,4-dicyanobenzene promoted decarboxylative formation of the C11-bridgehead radical, which cyclized into the 7-membered B-ring with stereoselective installation of the C9,10-tertiary carbons of 8a.