Iterative Stereospecific Reagent-Controlled Homologation Using a Functionalized α-Chloroalkyllithium: Synthesis of Cyclic Targets Related to Epibatidine
journal contributionposted on 18.03.2011 by Christopher R. Emerson, Lev N. Zakharov, Paul R. Blakemore
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Enantioenriched 1-chloro-2-(1,3-dioxolan-2-yl)ethyllithium was generated by PhLi initiated sulfoxide-ligand exchange and deployed in situ for sequential double stereospecific reagent-controlled homologation (StReCH) of B-(2-chloro-pyrid-5-yl) pinacol boronate. This process afforded highly functionalized contiguous stereodiad motifs (typically, % ee ≥ 98%, dr ≥ 85:15) amenable to subsequent annulative transformations as demonstrated by the concise synthesis (5−7 steps) of cyclic adducts related to the analgesic alkaloid epibatidine.