The alpha–methylene–gamma–butyrolactone skeleton belongs to a group of natural compounds, which are called sesquiterepenes. These compounds, have already been known to possess biological activities for example antitumor, antimicrobial, allergenic, etc. Here a new route to synthesize of this skeleton is reported using allybenzene and premade cobaloxime catalyst in three steps, such as bromoetherification of alkene , cyclization in the presence of cobaloxime and ultimate oxidation lead to preparation of target alpha–methylene–gamma–butyrolactone. Main products were isolated and characterized via IR, 1HNMR and GC-Mass.