Synthesis of Cavicularin and Riccardin C

Significance

Cavicularin is a strained macrocycle isolated from the liverwort Cavicularia densa in which ring A distorts out of the plane by 15° so as to adopt a boat-like conformation. Harrowven and co-workers circumvented the kinetic and thermodynamic barriers associated with formation of this strained system by employing an intramolecular radical addition/ring contraction to generate the dihydrophenanthrene in E. The process was accompanied by reduction of the aryl radical to give Riccardin C, a metabolite of the liverwort Reboulia hemisphaerica that displays in vitro cytotoxicity against nasal epidermoid carcinoma cells and inhibition of HIV-1 reverse transcriptase.