Intramolecular [6 + 4] and [4 4+ 2] Tropone-Olefin Cycloaddition Reactions. Facile Synthesis of the Ingenane Ring System

The intermolecular [6 + 4] and [4 + 2] cycloaddition reactions of tropone with dienes and monoenes, respectively, have been extensively examined and exploited in recent synthetic endeavors. Surprisingly, there has not been an investigation of the intra- c All new compounds reported herein exhibited satisfactory spectral (IR, NMR), analytical, and/or high-resolution mass spectral characteristics. Contaminated by ~10% tropone 17 (¹³C NMR analysis). Yield based on recovered starting material (4%) and product contaminated with 18 (6%, ¹H NMR analysis). Yield based on recovered starting materials (10%) and product contaminated with 18 (3%, 1H NMR analysis). Yield based on recovered 21 (42%).