Cyclophanes photochemical synthesis

The deselenization of 17 succeeded photochemically in 52% yield [28] (for comparison The direct synthesis of this [2.2]cyclophane from the corresponding benzylic bromides and phenyllithium yielded only 5.7% [30]). 

An efficient route for the synthesis of [2.2]cyclophanes has also been described which involves the photochemical double decarbonylation of the diketones (160), (161) and (162). The reactions are carried out in argon-degassed benzene solution and give high yields of products efficiently. In the case of the meta systems (160) both mono (163) and double decarbonylation products (164) are formed, but with (161) and (162) only the bisdecarbonyla-tion is observed affording (165) and (166) respectively. 

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... 

A surprisingly efficient intermolecular photochemical [2 + 2] dimerization was achieved in the synthesis of belt-shaped cyclophanes by irradiation of arenoannelated [18]annulenes like 176 [116]. The highly selective threefold [27t+27t] cycloaddition yields dimers 177 in up to 68%. The efficiency of this dimerization process even at high dilution can be explained with the perfect preorganization of the discotic mesogenes 176. 

Nishimura J, Nakamura Y, Hayashida Y, Kudo T (2000) Stereocontrol in cyclophane synthesis a photochemical method to overlap aromatic rings. Acc Chem Res 33(10) 679-686... 

Unless they have considerable strain in their ring systems, cyclophanes can be formed by most conventional bond-forming reactions. The first photochemical approach was applied by Schonberg et al. to prepare cage compound 1, a cyclophane, in 1968. Moreover, styrene photocyclodimerization (Scheme 1) was also published in the same year, > although it took almost two decades before we first successfully applied the reaction to cyclophane synthesis." The mechanism (Scheme 1) of [2 + 2] cycloaddition with direct photoirradiation of vinylarenes and their derivatives has been published."... 

Okamoto, H., Kimura, M., Satake, K., and Morosawa, S., Synthesis and adiabatic photochemistry of a 1,4-difluorobenzene-naphthalene biplanemer. Bull. Chem. Soc. Jpn., 66, 2436,1993. Nishimura, J., Nakamura, Y., Hayashida, Y., and Kudo, T, Stereocontrol in cyclophane synthesis a photochemical method to overlap aromatic rings, Acc. Chem. Res., 33, 679, 2000. 

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