Ring C Functionalized Diterpenoids. Part I. The Hypoiodite Reaction as a Route to Ring C Functionalized Kauranes and Phyllocladanes

Abstract

16β-ent-17-Kauranol (1a), the corresponding C-19 ester (1b), and 16β,17-phyllocladanol (2), on reaction with lead tetraacetate – iodine in refluxing cyclohexane, suffered intramolecular attack mainly at C-11. Thus1a gave as major products the 11-en-17-ol (3a) and the 11β-iodo-12β,17-ether (4a), along with minor amounts of the 9,11-en-12β,17-ether (5), the 11β,17-ether (6a), and, resulting from attack at C-12, the 12β,17-ether (7). The phyllocladanol 2 gave the 11β,17-ether (8) and the 9,11-en-12β,17-ether (9). The assignment of structures 6a, 7, and 8 to the ethers rests on their conversion with ruthenium tetroxide into the corresponding lactones, 10, 11, and 12.