AbstractThe attack of an oxy radical (produced by the hypoiodite reaction) on a tertiary hydrogen atom, followed by base treatment, leads to an allylic ether: a 4α‐hydroxy‐5 βH‐steroid gives a Δ‐4α, 9α‐oxide as the main reaction product. It is postulated, that in cases where the initial 1,5‐hydrogen shift from carbon to oxygen leads to a sterically hindered carbon radical, the iodine atom does not combine with the radical. By transfer of an electron from carbon to iodine an ion pair is formed which decomposes by elimination of HI. The final allylic ether is produced by addition of a newly formed oxy radical to this double bond, followed by another oxidation and/or substitution elimination reaction.