Divergent Syntheses of (-)-Chicanine, (+)-Fragransin A₂, (+)-Galbelgin, (+)-Talaumidin, and (+)-Galbacin via One-Pot Homologative <i>γ</i>-Butyrolactonization

Abstract

In this study, the divergent syntheses of (-)-chicanine, (+)-fragransin A2, (+)-galbelgin, (+)-talaumidin, and (+)-galbacin are detailed. In this approach, an early-stage modified Kowalski one-carbon homologation reaction is utilized to construct the central γ-butyrolactone framework with the two necessary β,γ-vicinal stereogenic centers. The two common chiral γ-butyrolactone intermediates were designed to be capable for assembling five different optically active tetrahydrofuran lignans from commercially available materials in a concise and effective divergent manner in five to eight steps. These five syntheses are among the shortest and highest-yielding syntheses reported to date.

Keywords

• one-pot homologative γ-butyrolactonization
• tetrahydrofuran lignans
• (-)-chicanine
• (+)-fragransin A₂
• (+)-galbelgin
• (+)-talaumidin