In summary, we have developed a site-, regio-, and diastereoselective 2+2 cycloaddition of non-symmetrical boron containing dienes. Systematic changes of the model system enabled 4+2 cycloaddition via extension of the chromophore, while the strategic incorporation of an additional boron unit, mitigated aggregation and enhanced reactivity. Boron hybridization proved to be ineffective, in contrast to current state of the art, in modulating EnT, yet revealed counterintuitive regiodivergence between geometric isomerization and 2+2 cycloaddition EnT processes. In-depth mechanistic analyses demonstrated a rapid site-selective geometric isomerization generating a photostationary state equilibrium between isomers, while computational investigations determined the Curtin-Hammett principle promotes preferential reactivity of the E-biradical with an alkene to forge specifically the target cycloadducts. Importantly, while spin density is effective in predicting electron density upon excitation, it's ability as a predictive tool, in step-wise energy transfer processes was shown to be obsolete. It is envisaged the developed insights will serve as a blueprint for the future discovery of divergent platforms utilizing non-symmetrical dienes under EnT catalysis.