Cyclophane diastereoselectivity

Timmermans et al. report that diastereoselectivity can be induced in the intramoleuclar meta photocycloaddition of ethenes to the benzene ring as a result of minimisation of steric interactions between substituents on the linking tether of the bichromophore and a methoxy group at the 2-position of the arene unity this type of photoprocess has also been used as a key step in a formal synthesis of crinipellin B (Wender and Dore). New polycyclic cage compounds 43 have been obtained by irradiation of the [3.3,3] (1,3,5) cyclophane 44 (Sakamoto et al.) and Kubo et al. have described the intramolecular [3 + 2] photocycloaddition of bichromophores such as 45 which gives rise to nine- to eleven-membered ring systems 46. 

Dienes 19 and 20 only react with A-phenylmaleimide (21) when the reactions are activated by high pressure cycloadditions with the more reactive dienophile 1 also occur under thermal conditions, but in lower yield. The reactions are totally a ft-(with respect to the unsubstituted benzene ring of the para-cyclophane unit ) enc/o-diastereoselective. DDQ oxidation of cycloadduct 24 led to the aromatized compound 26 while the aromatization of 23 and 25 failed. Interestingly, the cycloaddition between 1 and 19 led to the aromatized compound 22 this clearly indicates that 1,4-benzoquinone also acts as an oxidant. 

Thus, the effects of a tether combined with electronic interactions between reactants results in highly diastereoselective singlet excited state reactions, as shown by our results and the results of the cyclophane studies. In a similar... 

---