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A Concise Total Synthesis of (+)-Tetrabenazine and (+)-α-Dihydrotetrabenazine



Highly concise asymmetric total syntheses of (+)-tetrabenazine (1), a drug for the treatment of chorea associated with Huntington’s disease, and of (+)-α-dihydrotetrabenazine (2), an active metabolite of 1, have been accomplished. Our synthetic route features a trans-selective enol etherification, followed by an unprecedented cation-dependent aza-Claisen rearrangement to establish the carbon framework and two stereogenic centers of tetrabenazine. The syntheses consist of seven steps (34 % overall yield) for (+)-2 and eight steps (22 % overall yield) for (+)-1.