<h2>Summary</h2> The stereodivergent total synthesis of all stereoisomers of bioactive natural compounds to enable complete evaluation of stereochemical structure-activity relationships is highly challenging and valuable. Naturally occurring flavaglines, containing a compact functionalized cyclopenta[<i>b</i>]benzofuran scaffold, display a wide range of biological activities. Herein, we disclose a novel stereodivergent allylic alkylation of benzofuran-3(2<i>H</i>)-one that relies on the synergistic catalysis of a chiral <i>N</i>,<i>N</i>′-dioxide-Co(or Ni) complex and a phosphoramidite-Ir catalyst. All four possible stereoisomers of the α-allylated product are provided with excellent diastereo- and enantioselectivities by appropriate permutations of the two chiral catalysts. The concise synthesis of the targeted molecule rocaglaol is furnished in a stereodivergent manner, following a uniform synthetic route and using the same set of starting materials. Subsequently, a preliminary study on the anticancer activity for eight stereoisomers of rocaglaol reveals the pronounced influence of stereochemistry variations on biological activity.