Pentafulvene for the Synthesis of Complex Natural Products: Total Syntheses of (±)-Pallambins A and B

The first total syntheses of pallambins A and B are enabled by the use of pentafulvene in an unprecedented Diels–Alder reaction. After elaboration of the adduct through chemoselective cyclopropanation, strategic CH insertion affords the dense tetracyclic core of the natural products. 1,3‐Dipolar cycloaddition and palladium(II)‐catalyzed alkoxycarbonylation were leveraged for the construction of the hexacyclic scaffold en route to both natural products. Core congestion: The first total syntheses of the diterpenoids (±)‐pallambins A and B are reported. The use of fulvene in a Diels–Alder cycloaddition is without precedence in complex synthesis and enables, in combination with a strategic CH insertion, rapid assembly of the tetracyclo[4.4.03,5.02,8]decane core.