A photocycloaddition/fragmentation approach toward the 3,12-dioxatricyclo[8.2.1.0(6,13)]tridecane skeleton of terpenoid natural products.

Starting from tetronate 1 (R = CH(2)OH), a short photochemical access to the 3,12-dioxatricyclo[8.2.1.0(6,13)]tridecane-skeleton 2 of briarellin and asbestinin diterpenes has been explored. In the course of these studies, a number of surprising observations were made. For example, a two-step reaction pathway to the bicyclic ketolactone 3 was discovered, which is based on tetronate 1 (R = COOMe).