A highly stereospecific total synthesis of (±)-sesquicarene was accomplished by the photochemical transformation of the bicyclo[3.2.2]nona-3,6-dien-2-one (7), which was derived from 2-methyltropone (5), into the bicyclo[4.1.0]hept-2-ene (3).
Rearrangement Approaches to Cyclic Skeletons. I. Photochemical Rearrangement Approaches to (±)-Sesquicarene and (±)-Sirenin, [3–6] Fused-Ring Sesquiterpenes
The 4-alkyl, 4-alkenyl, and 4-aryl derivatives of bicyclo[3.2.2]nona-3,6-dien-2-one (9) were prepared from 9 itself by ultrasound-promoted Barbier reaction followed by PCC oxidation. Photochemical transformation of the 4-(4-methyl-3-pentenyl) derivative of 9, namely 13, in THF–water gave endo-7-[exo-7-(4-methyl-3-pentenyl)bicyclo[4.1.0]hept-2-ene]acetic acid (14). Acid 14 was converted into endo-7