Intermolecular Radical Cation Diels–Alder (RCDA) Reaction of Bicyclooctadienes: Biomimetic Formal Total Synthesis of Kingianin A and Total Syntheses of Kingianins D, F, H, and J

Three
endo bicyclooctadienol dimers corresponding to kingianins
A and H, D, and F and J were obtained by the intermolecular radical
cation Diels–Alder (RCDA) reaction. Each isomer was cleanly
isolated without the aid of preparative HPLC. Kingianins D, F, H,
and J were prepared by way of these intermediates from commercially
available materials in 10, 13, 9, and 17 steps, respectively. Kingianin
A has already been prepared from one of these compounds. Completion
of the synthesis of kingianin H relied on Manchand’s one-step,
three-carbon homologation.