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.