Fe(II)-mediated fragmentation of 1,4-diaryl-2,3-dioxabicyclo[2.2.2]octanes through competitive single electron transfer pathway and Lewis acid pathway

Reactions of 1,4-diaryl-2,3-dioxabicyclo[2.2.2]octanes 1a–d (1a: Ar=p-FC6H4, 1b: Ar=Ph, 1c: Ar=p-MeC6H4, 1d: Ar=p-MeOC6H4) with FeBr2 in THF afforded 1,4-diarylbutan-1,4-diones 2a–d and 1,4-diaryl-7-oxabicyclo[2.2.1]heptanes 3a–d. On the other hand, 4-aryl-3-cyclohexenones 4c–d and p-substituted phenols 5c–d were obtained in the reactions of 1c–d with FeBr2 in CH2Cl2. A new fragmentation mechanism involving an electrophilic oxyl radical 1,5-substitution and a nucleophilic O-1,2-aryl shift is proposed based on the product analysis. In addition, the in vitro antimalarial activities of 1a–d were tested.