Convergent synthesis of the common FGHI-ring part of ciguatoxins

Convergent synthesis of the common FGHI-ring part (54) of ciguatoxins was achieved via the following key steps: (i) the Nozaki-Hiyama-Kishi reaction connecting the F-ring part (6) with the I-ring part (7); (ii) regio- and stereoselective epoxidation; (iii) the 6-exo-epoxide opening reaction forming simultaneously the H-ring and the quaternary asymmetric center at C30; (iv) inversion of the C29 stereocenter by a two-step oxidation/reduction process, where the successful inversion depended on proper management of the steric environment of the substrate; and (v) final reductive cyclization constructing the G-ring.