A Concise Total Synthesis of (-)-Mesembrine.

A concise total synthesis of mesembrine (four steps from known compound) was achieved both racemically and asymmetrically. Two key reactions were used here. One is the Rh(I)-catalyzed [5 + 1] cycloaddition of vinylcyclopropane 3c and CO. The other one is Buchwald's Pd-catalyzed coupling reaction that coupled β,γ-cyclohexenone 2c with aryl bromide 5 (using dppe ligand for racemic or (S)-Antphos ligand for asymmetric synthesis) to give γ,γ-disubstituted α,β-cyclohexenone 1c. Finally, aza-Michael addition converted 1c to mesembrine.