Synthesis of epoxyoxirano- and epoxydihydroxyisoindolones

1-Oxo-3a,6-epoxyisoindolones oxidized with potassium permanganate to give 4,5-dihydroxy-3a,6-epoxyisoindolones, while oxidation with peroxyformic acid or 3-chloroperoxybenzoic acid yielded 2,6a-epoxyoxirano[e]isoindolones. Oxidation proceeded with selective formation of exo-cis-adducts.