Convergent Total Synthesis of Paecilomycin B and 6'- epi-Paecilomycin B by a Barbier-Type Reaction Using 2,4,6-Triisopropylphenyllithium.

Abstract

The convergent total synthesis of the natural product paecilomycin B and its 6'-epimer was investigated. The aryl- C-glycoside skeleton was constructed by an intramolecular Barbier-type reaction using 2,4,6-triisopropylphenyllithium and subsequent deoxygenation of the resulting anomeric hydroxy group. Starting from aryl iodide 24, the addition reaction afforded the thermodynamically stable C-β macrocyclic adduct 41a in 29% yield and the C-α adduct 41b in 1% yield. Meanwhile, aryl iodide 43 (6'-epimer of 24) gave only the C-α adduct 44 in 76% yield. The stereoselectivities of these nucleophilic addition reactions are also discussed.