Incorporation of oxygen atom in organic molecules causes significant changes in chemical and biological properties. In this way, we aim to synthetize natural products by increasing the oxidation level of complex diterpenes like the ent-kaurane kaurenoic acid (1) and the ent-beyerane isosteviol (9). The dihydroxylation of 1 using OsO4 and NMO gave 5 in 65%. The selective acetoxylation of 5 delivered 6 in 84%. Allylic oxidations of 1 and 2 with Py2Se2 and PhIO2 gave 7 and 3 in 35% and 55% yield, respectively. Enones 7 and 3 were submitted to dihydroxylation, delivering 8 and 4 in 44% and 75% yield, respectively. To the best of our knowledge, these are the first syntheses of natural products 4, 6, and 8.
While the remote oxidation of ent-kaurenes using Mn(CF3PDP) gave a complex mixture of oxidized products, ent-beyerane isosteviol methyl ester (10) as starting material delivered compounds 11 and 12 under the conditions developed by the White research group.