Autoxidation of 4-oxo-carotenoids in the presence of potassium t-butoxide gives the corresponding diosphenols (3, 4-didehydro-3-hydroxy-4-ones). These on reduction with potassium borohydride give the 3, 4-dihydroxycompounds which, on carefully controlled oxidation, yield the 3-hydroxy-4-ones. Astaxanthin (3, 3′-dihydroxy-ββ-carotene-4, 4′- dione), phoenicoxanthin (3-hydroxy-β, β-carotene-4, 4′-dione), and hydroxyechinenone ...