Total Synthesis of (-)-Dimatairesinol via Regioselective Intermolecular Oxidative Phenol Coupling.

We report the total synthesis of (-)-dimatairesinol, a new dimeric natural lignan possessing a unique interconvertible biaryl skeleton coupled at C-5/C-5 of two units of dibenzyl γ-butyrolactone lignan, namely, matairesinol. The key step involved high regioselective formation of a C-5/C-5 biaryl bond between two units of chiral phenolic γ-butyrolactone (R = H) via a direct and metal-free oxidative phenol coupling mediated by PIFA. On the contrary, C-6/C-6 biaryl coupling exclusively took place when nonphenolic γ-butyrolactones (R ≠ H) were employed, providing the corresponding biaryl products as atropisomers. Synthetic manipulations on the C-5/C-5-biaryl intermediate led to (-)-dimatairesinol.