Alcaloïdes Indoliques XI. Configuration absolue de la voacarpine

A correlation between voacarpine (I) and 16-epivobasine (II) establishes the absolute configuration at C5 and C15 and the geometry of the ethylidene side chain in voacarpine and in Nβ-methylvoacarpine (VI). This last base is shown to be identical with Le Men's vincadiffine.