In domino reactions, the product formed in one step undergoes a subsequent transformation under identical reaction conditions. Owing to the spontaneous nature of these reactions, it is difficult to isolate the key intermediates, and these are thus usually presumed. Here we perform a photoinduced domino reaction consisting of three photochemical steps. First, oxidative photocyclisation of a tetrafluorostilbene derivative generates tetrafluoro[7]helicene, which readily undergoes a photoinduced intramolecular Diels-Alder reaction. The resulting product then undergoes a double fluorine atom transfer under the same photochemical conditions. As a result, the four originally adjacent fluorine atoms are separated into two pairs in the final product. One advantage of a photochemical domino process over a thermal one is that the process can be suspended and restarted. Hence, precise control of the irradiation time allows us to isolate the thermally stable intermediates and characterise them using X-ray crystallography, thus confirming the until-now putative domino process.

The intramolecular Diels−Alder reactions of helicenes deform their π‐conjugated screw‐shaped skeletons. In particular, terminally tetrafluorinated [7]helicene (F4‐[7]helicene) undergoes a photoinduced Diels−Alder reaction followed by a photoinduced double fluorine atom transfer. Herein, we thoroughly investigated this photochemical domino process by decreasing the level of fluorine substitution. F3‐[7]Helicenes bearing two fluorine atoms at the dienophile terminal underwent photoinduced Diels−Alder reactions, but the whole domino process became slow. F2‐[7]Helicene, which is difluorinated only at the dienophile terminal, was also photolabile. As a result, two fluorine atoms were sufficient for the photochemical domino reaction to occur. X‐ray crystallographic analysis revealed that F2‐[7]helicene was less compressed than F4‐[7]helicene, indicating that terminal polyfluorination enhanced the intramolecular arene−fluoroarene stacking interactions and thus promoted the transformations.

Tri‐ and tetra‐fluorinated [7]helicenes are photolabile and undergo a double fluorine atom transfer. Herein, we show that the transferred product further undergoes a skeletal transformation on silica gel. The transformation begins with activation of the allylic C−F bond on the silanol surface. Then, the resulting carbocation readily undergoes a regioselective nucleophilic aromatic substitution with water, depending on the position of the fluorine substituents. Hexafluoro‐2‐propanol also activated the allylic C−F bond and acted as a nucleophile. These findings support the generation of a highly reactive cationic electrophilic intermediate in the successive transformations involving fluorine atoms.