Intramolecular cyclophanes, photochemical

Stilbene and its derivatives have often been used in photochemical [2-1-2] cycloadditions. The intermolecular dimerization presented by H. Meier of 2,3-fcij(2-phenylethenyl)-naphthalene directly leads to cyclophane via two [2-1-2] cycloadditions in one step. The yield is surprisingly very high and comparable with those of intramolecular reactions presented by W. H. Laarhoven. Various examples of vinylstilbenes are photolyzed to form cyclobutanes via a "crossed" addition. Even [2a-H2jt] cycloadditions and rearrangements involving H-transfer are utilized to construct unusual bicyclic or tricyclic compounds. 

Although the [2 + 2] photocycloaddition is preferably prevented in the synthesis of PAHs, it has been proven to be a very feasible approach in the selective synthesis of syn-[2.2]cyclophanes [86,87]. Topological reaction control in solution has been achieved for a multistep intramolecular [2 + 2] cycloaddition reaction in the photochemical formation of [n]-ladderanes from pseudo-gem-bis(polyene) substituted [2.2]paracyclophanes [88]. The probably most well-known example of an intramolecular photocycloaddition process is one of the... 

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