Recursive Anionic γ'-Spiro-annulation of Cyclic Vinylogous Esters with 2-Vinylbenzoates

Abstract

We report a γ'-selective anionic cascade spiroannulation between cyclic vinylogous esters (CVEs) and 2-vinylbenzoates. This transformation proceeds with high γ'-selectivity, enabling CVEs to function as γ',γ'-dianionic equivalents while engaging 2-vinylbenzoates as an unconventional 1,5-dielectrophilic partner. Mechanistically, this behavior is attributed to two sequential deprotonations at the γ'-position of the CVE, enabling a recursive anionic activation process. The reaction is efficiently promoted by KOtBu in the presence of a Cu(I) salt in DMF under thermal conditions. This method enables rapid construction of densely functionalized spirocarbocyclic scaffolds with high structural complexity.