Dione 2 can then undergo an intramolecular photochemical [2+2] cycloaddition, which is promoted by the use of either a high-powered Hg lamp or a UV-B lamp (λexc = 311 nm) under acidic conditions and has been successfully scaled-up using continuous flow photochemistry. After being refluxed in water to hydrolyse any methyl ketals, 3 can then be transformed into the cubane scaffold using a Favorskii rearrangement to give cubane-1,4-dicarboxylic acid 4, which is then esterified and isolated as 1. Scheme 1. (A) Body diagonals of cubane and benzene. (B) Overall synthesis for dimethyl cubane-1,4-dicarboxylate.