Efficient Synthesis of the (buta-2,3-dienyl)carboxamide of Isopimaric Acid and the Potential of This Compound towards Heterocyclic Derivatives of Diterpenoids.

The -(2,3-butadienyl)carboxamide of isopimaric acid, that is, compound , was prepared through a two-step synthetic procedure starting from the natural diterpene isopimaric acid. The Pd-catalyzed cross-coupling and subsequent cyclization of terpenoid allene with several aryl iodides and aryl bromides gave access to optically active diterpenoid-oxazoline derivatives in good to excellent yields. The functional group tolerance in the aryl iodides was demonstrated by several examples, including substrates with additional --butoxycarbonyl-protected amino, hydroxy, and carboxy substituents in the position.