Regioselective synthesis of bridged azabicyclic compounds using radical translocations/cyclisations of methyl 2-alkynyl-1-(o-iodobenzoyl)pyrrolidine-2-carboxylates: a formal total synthesis of (±)-epibatidine

Abstract

Bu₃SnH-mediated radical translocations/cyclisations of methyl 2-alkynyl-1-(o-iodobenzoyl)pyrrolidine-2-carboxylates have been examined. The 2-[3-(trimethylsilyl)prop-2-ynyl]-8,2-[4-(trimethylsilyl)but-3-ynyl]- 14, and 2-[5-(trimethylsilyl)pent-4-ynyl]-pyrrolidine derivatives 18, upon treatment with tributyltin hydride in the presence of azoisobutyronitrile in boiling toluene gave, regioselectively, the 7-azabicyclo[2.2.1]heptane 19, 8-azabicyclo[3.2.1]octane 23, and 9-azabicyclo[4.2.1]nonane 26, respectively. The method has been applied to a formal total synthesis of (±)-epibatidine.