Topochemical control of the photodimerization of aromatic compounds by γ-cyclodextrin thioethers in aqueous solution.
The formation of soluble 1:2 complexes within hydrophilic γ-cyclodextrin (γ-CD) thioethers allows to perform photodimerizations of aromatic guests under controlled, homogenous reaction conditions. The quantum yields for unsubstituted anthracene, acenaphthylene, and coumarin complexed in these γ-CD thioethers were found to be up to 10 times higher than in the non-complexed state. The configuration of the photoproduct reflected the configuration of the dimeric inclusion complex of the guest. Anti-parallel orientation of acenaphthylene within the CD cavity led to the exclusive formation of the anti photo-dimer in quantitative yield. Parallel orientation of coumarin within the complex of a CD thioether led to the formation of the syn head-to-head dimer. The degree of complexation of coumarin could be increased by employing the salting out effect.
Organic Macromolecular Chemistry, Saarland University, Campus Saarbrücken C4 2, 66123 Saarbrücken, Germany.
Hai Ming
HM
Wang
Gerhard
G
Wenz
acenaphthylene; anthracene; coumarin; cyclodextrins; photodimerization; quantum yield; stereoselectivity