Photo-promoted one-pot coupling isomerization–codimerization of norbornadiene for the efficient synthesis of liquid fuel with a density higher than 1 g mL−1

Abstract

exo–exo-Hexacyclo[9.2.1.0^2,10.0^3,7.0^4,9.0^6,8]tetradec-12-ene (exo–exo) is one of the few liquid fuels with a density higher than 1 g mL⁻¹. Currently, exo–exo can only be synthesized in bulk via codimerization of norbornadiene (NBD) and quadricyclane (QC). However, QC is expensive and unstable, which makes it uncompetitive as a raw material. In this work, one-pot synthesis of exo–exo solely from NBD is achieved by coupling NBD isomerization and NBD–QC codimerization. The multicomponent catalyst system and reaction conditions are fully optimized by the Bayesian method for improving exo–exo yield. Under efficient coupling in one pot, NBD conversion and exo–exo selectivity reach 92.6% and 81.0%, respectively. Moreover, the kinetics of the one-pot coupling reactions are investigated and compared with those of the corresponding single reaction. Finally, the catalytic mechanism is investigated, and the origin of significantly improved efficiency in coupling reactions is revealed to be UV illumination.