[2+2] and [2+1] cycloaddition of myrcene for synthesis of highly strained bio-fuels with high density and high impulse

Developing bio-fuels provides a sustainable strategy to reduce the dependence on finite fossil fuels. But biomass-based fuel molecules usually lack strained structure, resulting in undesirable density and impulse for aerospace applications. Herein, the highly strained bio-fuels are synthesized from myrcene by photoinduced [2 + 2] cycloaddition and hydrogenation/cyclopropanation reactions. The triplet energy transfer mechanism is revealed through theoretical calculations, triplet quenching experiments and phosphorescent measurement. The reaction conditions of photocycloaddition reaction are optimized, including the photosensitizer type and amount, solvent effect, substrate concentration, reaction temperature and light intensity. Under the optimal conditions, the yield of target photocycloaddition product reaches ca. 82.61 %, which is then hydrogenated and cyclopropanized to two kinds of bio-fuels, namely PC@HG and PC@CP, respectively, which have high density of 0.836 and 0.886 g mL⁻¹, high impulse of 326.71 and 329.42 s, superior cryogenic properties, and good combustion properties. This work provides a feasible pathway for the preparation of highly strained bio-fuels with high density and high impulse.