Total syntheses of naturally occurring antiviral indolosesquiterpene alkaloids, xiamycins C-F Csp-H functionalization.

Concise total syntheses of naturally occurring antiviral indolosesquiterpene alkaloids, xiamycin C (2a), D (2b), E (2c) and F (2d), have been achieved a late-stage oxidative δ-Csp-H functionalization of an advanced pentacyclic enone intermediate 8. This strategy takes advantage of -nitration of naturally occurring abietane diterpenoids to synthesize -bromo nitroarene derivative 11. A Suzuki-Miyaura coupling of 11 with phenylboronic acid followed by Cadogan's ring closure provided a modular approach to a carbazole ring required for a functionalized pentacyclic core of indolosesquiterpene alkaloids.