Regioselective Synthesis of Spiro- <i>Ganoderma</i> Meroterpenoid Motifs via Lewis Acid-Catalyzed Divergent Cycloadditions: [3 + 2] and Water Accelerated [5 + 2] Annulations

For the first time, a water-driven Lewis acid-catalyzed [5 + 2] cyclization between allylsilanes and aurones was developed, affording spiro-<i>Ganoderma</i>-meroterpenoid (SGM) motifs with high yields and stereoselectivity. This method enables efficient construction of spiro-tricyclic rings, introducing contiguous stereocenters without dry conditions or thermal/photoactivation. This approach revealed dual catalysts over the regio-control [3 + 2] spirocyclic ring creation by opposite functional group incorporation and halting at the interim stage, facilitating the synthesis of SGM scaffolds.