Stereoselective\nApproach to the Core Structure of\n(+)-Phainanoid A via Strategically Engineered Cascade Polyene Cyclization

Stereoselective synthesis of <b>3b</b> and its\ncascade polyene\ncyclization to <b>18b</b> have been described. Acyclic polyene <b>3b</b> was prepared from allyl bromide <b>4</b> and 1,3-dithiane <b>5</b>, and intermediates <b>4</b> and <b>5</b> were\nsynthesized from the commercially available geraniol (<b>6</b>) and cyclopenten-2-one (<b>8</b>), respectively, using enantioselective\nreduction of ketone, Johnson–Claisen rearrangement, and the\nSuzuki reaction as key steps. Au­(I)-mediated diastereoselective polyene\ncyclization of <b>3b</b> efficiently afforded tetracyclic compound <b>18b</b>.