Rearrangement Approaches to Cyclic Skeletons. I. Photochemical Rearrangement Approaches to (+/-)-Sesquicarene and (+/-)-Sirenin, Fused-Ring Sesquiterpenes

Article abstract of DOI:10.1246/bcsj.58.211

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 the THF-water gave endo-7-hept-2-ene>acetic acid (14).Acid 14 was converted into endo-7-methyl-exo-7-(4-methyl-3-pentenyl)bicyclo<4.1.0>heptan-2-one (4), a key intermediate of (+/-)-sesquicarene and (+/-)sirenin total syntheses.Futhermore, a highly stereospecific total synthesis of (+/-)-sesquicarene was acomplished by the photochemical transformation of the 1-methyl derivative of 13 prepared from 2-methyl tropone.