Ene reactions of allylically stannylated cholestenes: singlet oxygenation of 7α-triphenylstannylcholest-5-en-3β-ol, and of 7α-triphenylstannyl- and 7α-tributylstannyl-cholest-5-ene-3-one, and the rearrangement of 5α-tributylstannylperoxy-3β-benzoyloxycholest-6-ene and of 7α-tributylstannylperoxy-3β-benzoyloxycholest-5-ene

Abstract

The reaction of some allylically stannylated steroids with singlet oxygen has been investigated. 7α-Triphenylstannylcholest-5-ene-3β-ol reacts on the β-face with shift of the 4β-hydrogen to give 6β-hydroperoxy-7α-triphenylstannylcholest-4-ene-3β-ol, whereas cholest-5-ene-3β-ol itself reacts on the α-face to give 5α-hydroperoxycholest-6-ene-3β-ol.

7α-Triphenylstannyl- and 7α-tributylstannylcholest-5-ene-3-one give the corresponding 6β-hydroperoxy-7α-stannylcholest-4-ene-3-one (50–55%), together with the 4,6-dien-3-one which is formed by elimination. In contrast, the parent cholest-5-en-3-one under the same conditions gives some of the 6β-hydroperoxy-4-ene-3-one, but the principal product is the hemiperketal from the 5α-hydroperoxycholest-6-ene-3-one.

In neither system was there any evidence for a metalloene reaction, nor for cycloaddition accompanied by a nucleophilic 1,2-shift of the tin.

3β-Benzoyloxy-5α-tributylstannylperoxycholest-6-ene undergoes the Schenck and Smith types of rearrangement by a radical chain mechanism to give successively the corresponding 7α- and 7β-stannylperoxy-5-enes.