Photoinduced Skeletal Rearrangements Reveal Radical-Mediated Synthesis of Terpenoids

Herein, we describe the protecting-group-free total synthesis of two structurally diverse Isodon diterpenoids, (+)-ent-kauradienone (3) and(-)-jungermannenone C (4), in 12 and 14 steps respectively, through sequential applications of three radical-based reactions, including the photoinduced skeletal rearrangements of bicyclo[ 3.2.1] octene ring systems. Further investigations of this photochemical radical rearrangement on a series of diverse terpenoids demonstrated both the unparalleled functional-group tolerance and the broad applicability of such late-stage photochemical rearrangements for the synthesis of structurally diverse and complex small molecules. Overall, the mild nature of late-stage photoinduced skeletal rearrangements might suggest that they are possible in a biological setting in unappreciated complimentary biosynthetic pathways.