Photoracemization of Blestriarene C and Its Analogs.

Two analogs of blestriarene C (4,4'-dimethoxy-1,1'-biphenanthrene-2,2',7,7'-tetraol) bearing no 7,7'-dihydroxy ( 3) and 4,4'-dimethoxy groups 4 were prepared. Unlike blestriarene C ( 1), compounds 3 and 4, as well as 1,1'-biphenanthrene-2,2'-diol ( 5), do not racemize under fluorescent lamp illumination. Cyclic voltammetry analysis reveals that compound 1 has a lower half-wave potential ( E1/2) than compounds 3, 4, 5, suggesting that a redox cycle is involved in the . Compound 1 racemizes by absorbing UV light corresponding to the 1 Lb band. During the reaction, no side products are observed. The is significantly inhibited under nitrogen. Based on these observations, we propose a feasible mechanism for the easy of compound 1, which is mediated by a cation radical generated in situ by a reversible photo-induced oxygen oxidation. Chirality 27:479-486, 2015. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]