Total Synthesis and Absolute Configuration Determination of the α‑Glycosidase Inhibitor (3<i>S</i>,4<i>R</i>)‑6-Acetyl-3-hydroxy-2,2-dimethylchroman-4-yl (<i>Z</i>)‑2-Methylbut-2-enoate from <i>Ageratina grandifolia</i>

Herein, we report the first total synthesis of α-glycosidase inhibitor (3R, 4S)-6-acetyl-3-hydroxy-2,2-dimethylchroman-4-yl (Z)-2-methylbut-2-enoate as well as its enantiomer. Our synthesis confirms the chromane structure separately proposed by Navarro-Vazquez and Mata, on the basis of DFT computations. Furthermore, our synthesis allowed us to determine the absolute configuration of the natural compound as (3S, 4R) and not (3R, 4S).