Photocycloadditions cyclodextrins

Wenz et al. have demonstrated that photoreactions are effective for the construction of polyrotaxanes (Scheme 18) [114]. In the knowledge that stil-benes undergo [2+2]photocycloaddition to yield cyclobutane derivatives by UV irradiation, they prepared a quaternary polymeric inclusion complex from /1-cyclodextrin, y-cyclodextrin, (E)-4,4-bis(dimethylaminomethyl)stil-bene (B), and (li)-stilbene polymer (A). Upon irradiation at 312 nm, the (E)-stilbene units of A underwent [2+2]photocycloaddition with B by catalysis of y-cyclodextrin to form the tetraphenylcyclobutane group, which acted as blocking group for /1-cyclodextrin. Wenz et al. claimed that this was the... 

Inoue et al, reported the intramolecular [4 + 4] photocycloaddition of 6A,6C-bis(2-anthracenecarboxylate) ester of a-cyclodextrin (a-CD) in water, which gave the antz-head-to-head cycloadduct (after base hydrolysis) in highly regio- and enantioselective manner in the presence of y-cyclo-dextrin (y-CD). " Diastereoselective photocyclodimers of ester of (249) tethered to cellulose were obtained. Saigo et al., found the diastereo- and enantio-selective photocyclodimerization of (249) and (250) by use of enantiopure amphiphilic amino alcohols as a matrix. The enantioselective photoreaction of (249) was also reported by Shinkai et al. (25Ia,b). 

The photodimerization of fran -cinnamic acid 30 in the presence of CB[8] studied by Ramamurthy et al. was discussed in Section 5.4 [121]. Prior to that report, they specifically examined the templating ability of CB[8] and y-cyclodextrin for this same dimeric photocycloaddition [127]. They also studied the templating action of CB[8] on the dimeric photocycloaddition of trans-1,2-bis(n-pyridyl)-ethylene 33 and other related olefins [128]. In the absence of CB[8], photoreaction of 33 produced only the monomer hydration product 34. However, in the presence of CB[8], 1 2 host guest inclusion complexes were formed, and upon irradiation gave predominantly (90%) the photodimerization product 35. These reactions are illustrated in Fig. 3.17. Thus, in this case,... 

Vizvardi, K., Desmet, K., Luyten, I., Sandra, P., Hoornaert, G., and Van der Eycken, E., Asymmetric induction in intramolecular meta photocycloaddition cyclodextrin-mediated solid-phase photochemistry of various phenoxyalkenes, Org. Lett., 3,1173,2001. 

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