Pioneering Constitutionally Isomeric Hydrocarbons via. Skeletal Rearrangements of a Unique Cage Diene Towards Acid-Catalyzed High-Energy Mechanisms

The study of cage compounds, unique polycyclic hydrocarbon architectures, is distinguished by distinctive strain energies and properties. Within this domain, the Etzkron group has achieved the third recorded synthesis, and the first optimized reaction, of pentacyclo[8.4.0.03,8.04,14.07,11]tetradeca-5,12-diene (4). Achieving the primary objective of this study through an acid-catalyzed rearrangement reaction of cage diene (4), the synthesis of novel constitutionally isomeric compound (7) was serendipitously discovered, with slow conversions (504 hours) and low yields (72% yield with 28% byproduct). Hence, the secondary goal: optimize reaction conditions—varying solvent choice, catalyst type, load, and temperature—to achieve enhanced efficiency. Refining the process with dichloroethane, triflic acid, and Amberlyst 15 at 87°C yielded 71% (7) with 6% byproducts in 5 hours, significantly progressing yield and selectivity. Therefore, a correlation between acidity and consequently byproducts was established, enabling the discovery of protonation being the driving factor of the reaction process. Thus emerged a unique mechanism featuring a nonclassical carbocation intermediate, providing enhanced regioselectivity. Derivatives of compound (7) through quantum computational chemistry show promise as the first chemical agent capable of not only encapsulating catalysts in high-energy systems—its distinctly stable core prevents degradation and the subsequent formation of toxic byproducts—but also generating a fifth of traditional rocket fuel’s power while being 1/170th of its molecular weight. With enhanced precision and efficacy crucial to advanced propulsion industries, (7) additionally plays a vital role in the protection of surrounding environments facing catalyst-driven HEDM reactions.