Our investigation commenced with the exploration of suitable photocatalysts, capable of promoting the single-electron oxidation of the BCB moiety. Olefin 2a, containing no adjacent heteroatom or radical stabilising group, was selected as the model coupling partner due to its presumed inactivity under any currently known BCB [2π+2σ] cycloaddition conditions. Upon screening photocatalysts across a wide range of oxidation potentials, it was demonstrated that [Mes2Acr t Bu2]ClO4 (E1/2 (PC*/PC •-) = +2.00 V vs SCE) , irradiated with blue LEDs, could catalyse the desired [2π+2σ] cycloaddition reaction with 2a (Fig. , entry 5). Indeed, it was observed that employing photocatalysts that display an excited state oxidation potential below +1.86 V (or significantly greater than +2.00 V) failed to deliver any observable product (entries 1-6). After an extensive exploration of the reaction conditions (see Supplementary Information for full optimisation details), it was found that improvements to the yield could be achieved upon increasing the equivalents of the alkene coupling partner and performing the reaction in MeNO2 (Fig. , entries 7-10). Although this reaction represents the first example of a bicyclo[1.1.0]butane [2π+2σ] cycloaddition with a simple alkyl substituted alkene, the overall yield is partially limited by the side reactions that can occur from the BCB radical cation, such as dimerisation . Finally, control reactions, in which the photocatalyst and light source were omitted, were performed (entries 11-12). The inability to access any cycloaddition product under these conditions clearly shows that product formation is dependent on the generation of the excited state photocatalyst and does not arise as a result of direct excitation of either the BCB or alkene substrates.