For example, depending on the specific substrates used, photoredox-catalysed hydrofunctionalisations of alkenes may involve initially either oxidation of the nucleophile or the alkene substrate; this mechanistic divergence may impact on the selectivity (e.g. regiochemistry) of the outcome. Overall, mechanistic complexity can hinder the rational design of new classes of photocatalytic reactions. In this study, we harnessed a high-throughput experimentation approach to enable the discovery of new classes of photocatalytic reactions (Figure ). We assembled a set of substrates that had at least one functional group that was precedented to react in a photocatalytic reaction. Crucially, however, only a few pairs of these functional groups were precedented to react together in photocatalytic reactions. Rather than being guided by any mechanistic rationale, we simply screened for reactions in which a specific combination of substrates and additives resulted in the formation of new products. Herein, we show that the approach enabled discovery of a novel dearomative [4+3] photocycloadditionoxidation, as well as the extension of [2+2] photocycloaddition to previously undescribed classes of alkene substrate. Furthermore, we showed that it was possible to optimise the [4+3] photocycloadditionoxidation into a viable method for the synthesis of complex bridged scaffolds from alternative aromatic substrates.