The Total Synthesis of (+)-Taxoquinone, (−)-7α-Acetoxyroyleanone, (−)-Dehydroroyleanone, (−)-Horminone, (−)-7-Oxoroyleanone, and (+)-Inuroyleanol

Abstract

Abstract Methylation of 12-benzoyloxyabieta-8,11,13-trien-11-ol with methyl iodide afforded 11-benzoyloxy-12-methoxyabieta- and 12-benzoyloxy-11-methoxyabieta-8,11,13-triene (9). Oxidation of the latter product with chromium trioxide, followed by sodium borohydride reduction and acetylation, gave 7β-acetoxy-12-benzoyloxy-11-methoxyabieta-8,11,13-triene (17) and its 7α-acetoxy isomer (18) in a ratio of ca. 5 : 1. On the other hand, treatment of 9 with lead tetraacetate produced 17 and 18 in a ratio oi ca. 1 : 2. The 7β-acetate (17) was then oxidized with chromium trioxide and the resulting p-quinone derivative was hydrolyzed with aqueous sodium hydroxide to give taxoquinone (1), which on dehydration gave dehydroroyleanone. Similarly, the 7α-acetate (18) was converted into horminone (4) via the p-quinone derivative, which was treated with aqueous sodium hydrogencarbonate to give 7α-acetoxyroyleanone. Oxidation of 4 with manganese dioxide afforded 7-oxoroyleanone. Methylation of 1 with diazomethane, followed by oxidation with a chromium trioxide-pyridine complex, afforded 12-methoxyabieta-8,12-diene-7,11,14-trione, which on reduction with sodium dithionite gave inuroyleanol.