Photochemical reactions are interesting in context of green chemistry. They do not need polluting or toxic reagents and offer a wide range of opportunities for synthesis of highly functionalized derivatives. The use of light energy provides efficient solutions for solving some problems that occur
during the ground-state reactions. The results reported herein refer to the efficient use of photochemical reactions in synthesis of norlabdanic compounds, including same natural analogues. For this, one-step photochemical degradation of side chain of methylketones derived from labdane diterpenoids Larixol and Sclareol was used. Next, dye-sensitized photooxygenation of resulted dienes gave unsaturated hydroperoxides and endoperoxides as result of ene-reaction and [4+2] cycloadditon of singlet oxygen. Reduction of the latter with appropriate reagent leads to highly functionalized drimanes (Figure 1).

Figure 1. Synthesis of norlabdanic compounds via photochemical transformations.
References: 1. E. L. Clennan. Tetrahedron, 2000, 56, 9151-9179. 2. E. L. Clennan. Tetrahedron, 2005, 61, 6665-6691.