Renewable Spirocyclic High-Density Fuel Synthesis via Self-Sensitized [2 + 2] Photocycloaddition of β-Pinene and Methyl Cyclopentenone

Abstract Renewable high-energy-density fuels hold substantial promise for advancing sustainable aviation. However, realizing this potential requires the development of effective strategies for constructing high-performance fuel molecules. Herein, this study reports the synthesis of high-density spirocyclic fuels via a feasible self-sensitized intermolecular [2 + 2] photocycloaddition of biomass-derived β-pinene and methyl cyclopentenone (MCP). Reaction conditions are systematically optimized, achieving an MCP conversion of 79.5% and a Co-adduct yield of 61.4%. Mechanistic investigations, including triplet quenching and radical trapping experiments, confirm that the reaction proceeds via a self-sensitized pathway involving triplet excited states and biradical intermediates. A kinetic model is established, revealing a linear correlation between the reaction rate and light intensity. After hydrodeoxygenation, a density of 0.949 g cm–3, a volumetric net heat of combustion of 40.46 MJ L–1 and an excellent freezing point (<−60 °C) are achieved for the synthesized spirocyclic fuel. Moreover, both the pure fuel and its blend demonstrated superior combustion, with minimum ignition temperatures of 280 and 275 °C, respectively, significantly lower than the reported value for JP-10 (380 °C). These results demonstrate the potential of structure-guided substrate screening and photochemical synthesis for developing high-performance biomass-derived fuels.