Asymmetric Synthesis of β-Substituted α-Methylenebutyrolactones via TRIP-Catalyzed Allylation: Mechanistic Studies and Application to the Synthesis of (S)-(-)-Hydroxymatairesinol

Asymmetric allylation of (hetero)aromatic aldehydes by a zinc(II)-allylbutyrolactone species catalyzed by a chiral BINOL-type phosphoric acid gave beta-substituted alpha-methylenebutyrolactones in 68 to >99% ee and 52-91% isolated yield. DFT studies on the intermediate Zn2+-complex - crucial for chiral induction - suggest a six-membered ring intermediate, which allows the phosphoric acid moiety to activate the aldehyde. The methodology was applied to the synthesis of the antitumour natural product (S)-(-)-hydroxymatairesinol.