Synthesis of the Pentacyclic Skeleton of the Indole Alkaloid Arboflorine

An effective synthesis of the pentacyclic core of the unusual Kopsia alkaloid arboflorine is reported. The success of the synthetic route rested on the use of a borylative C–H functionalization reaction, a convergent Suzuki cross-coupling to a C(2) halogenated indole, and an unprecedented transannular dehydrogenative C–N bond forming reaction.