Studies toward the total synthesis of armatol F: stereoselective construction of the C6 and C7 stereocenters and formation of the A-ring skeleton

Armatol F, isolated from the red alga Chondria armata as a polyether triterpene, has a solitary oxepane (A-ring) and a fused tricyclic ether moiety (BCD-ring). The A-ring features a rare cis-relationship between the hydroxy group at the quaternary carbon C6 and the carbon chain at C7. As part of our program toward the total synthesis of armatol F, a new stereoselective method for the construction of the C6 and C7 stereocenters has been developed based on chirality-transferring Ireland-Claisen rearrangement. The A-ring skeleton has also been synthesized from the rearrangement product by a process including ring-closing olefin metathesis.