A ring-closing metathesis-based approach to the synthesis of (+)-tetrabenazine.

A modular stereoselective synthesis of the vesicular monoamine transport inhibitors (+)-tetrabenazine ((+)-1) and (+)-α-dihydrotetrabenazine ((+)-2) has been developed. The approach is based on amine 4 and acid 5 as the key building blocks, which were elaborated into macrolactam 3 by amide coupling and a subsequent highly E-selective RCM reaction. Macrolactam 3 could be converted into tetrabenazine in three known steps.