Peroxide–diene oxygen transfer reactions induced by titanium tetrachloride

Catalysis of the reaction between triplet oxygen and ergosteryl acetate (I) by titanium tetrachloride unexpectedly affords 6α-chloro-5-hydroxy-5α-ergosta-7,22-dien-3β-yl acetate (III). This chlorohydrin is produced by a reaction between equimolar amounts of the 5,8-peroxide (II) and the acetate (I), the generality and mechanism of which are discussed briefly.