Visible light photoredox and Polonovsld-Potier cyclizations for the synthesis of (±)-5-epi-cermizine C and (±)-epimyrtine

Quinolizidine alkaloids epi-cermizine C and epimyrtine were synthesized from a common intermediate in 5-6 steps from commercially available materials. The key step involved an allylsilane cyclization with an iminium ion formed by oxidation of a tertiary amine. Oxidative annulation was promoted either catalytically by visible light photoredox catalysis or by stoichiometric Polonovski-Potier conditions. There was a modest difference in diastereoselectivity between the two methods, with photoredox providing the key quinolizidine intermediate in 4.7:1 dr versus 2:1 dr for the Polonovski route. (C) 2016 Elsevier Ltd. All rights reserved.