Trityl tetrafluoroborate and tris-(p-bromophenyl)aminium cation-radical are exceptionally effective catalysts for oxygenation of ergosteryl acetate (I; R = Ac) to the peroxide (II; R = Ac); the trityl cation catalysed reaction is a photo-oxygenation, whilst the aminium cation-radical catalysed reaction is thermal.
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BARTON et al. (1972) studied this question.