Bioinspired Synthesis of Pygmaeocins and Related Rearranged Abietane Diterpenes: Synthesis of Viridoquinone.

A bioinspired synthesis of rearranged abietane diterpenes, related to pygmaeocins, is described. In this process, the key step is the 1,2-migration of the C-20 angular methyl to the C-5 position of the abietane skeleton, which occurs when a C6-C7 unsaturated dehydroabietane derivative is treated with SeO2 in dioxane under reflux (19 examples for this rearrangement are described). Utilizing this reaction, an enantiospecific synthesis of pygmaeocin C and the first synthesis of viridoquinone, starting from the abietane phenol ferruginol, are reported. A tentative mechanism for this reaction and a possible biosynthetic pathway for this family of metabolites are postulated.