We investigate the DA reaction between cyclopentadiene and acrylonitrile (Scheme 1a). This reaction produces two distinct endo/exo isomers as products. Outside the cavity and under standard reaction conditions, the DA reaction is kinetically controlled and shows a nonselective result with 54% endo to 46% exo products. It has been recently proposed that this intrisically non-selective reaction can be made selective by coupling the ground state of the reacting molecules to an optical cavity with frequency in the range of electronic excitations (i.e., ω c ∼1-3 eV) in contrast to the recently explored vibrational polaritons (i.e., ω c ∼ 0.1 eV) To explore this effect, we apply the recently developed ab initio cavity quantum electrodynamics to further investigate this reaction and its properties under strong coupling.