Total Synthesis of the Herqulines

The herquline family of natural products were originally isolated from penicillium herquei in 1979 by the Ōmura group (see figure below). These strained macrocyclic alkaloids all contain multiple stereocenters, and an unsymmetrically substituted piperazine. Herqulines B and C feature two β,γ-unsaturated cyclohexenones, while herquline A bears an additional pyrrolidine. In the intervening years since their isolation, numerous failed synthetic approaches have been disclosed, and the primary synthetic hurdle appears to relate to the significant strain imparted by the macrocycle. In 2019 three successful total syntheses were reported (almost) concurrently, by the groups of Phil Baran, Corinna Schindler and John Wood. A complete overview of these syntheses will be provided.