ENE REACTIONS OF ALLYLICALLY STANNYLATED CHOLESTENES - SINGLET OXYGENATION OF 7-ALPHA-TRIPHENYLSTANNYLCHOLEST-5-EN-3-BETA-OL, AND OF 7-ALPHA-TRIPHENYLSTANNYL-CHOLEST-5-ENE-3-ONE AND 7-ALPHA-TRIBUTYLSTANNYL-CHOLEST-5-ENE-3-ONE, AND THE REARRANGEMENT OF 5-ALPHA-TRIBUTYLSTANNYLPEROXY-3-BETA-BENZOYLOXYCHOLEST-6-ENE AND OF 7-ALPHA-TRIBUTYLSTANNYLPEROXY-3-BETA-BENZOYLOXYCHOLEST-5-ENE

The reaction of some allylically stannylated steroids with singlet oxygen has been investigated. 7-alpha-Triphenylstannylcholest-5-ene-3-beta-ol reacts on the beta-face with shift of the 4-beta-hydrogen to give 6-beta-hydroperoxy-7-alpha-triphenylstannylcholest-4-ene-3-beta-ol, whereas cholest-5-ene-3-beta-ol itself reacts on the alpha-face to give 5-alpha-hydroperoxycholest-6-ene-3-beta-ol. 7-alpha-Triphenylstannyl- and 7-alpha-tributylstannylcholest-5-ene-3-one give the corresponding 6-beta-hydroperoxy-7-alpha-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 6-beta-hydroperoxy-4-ene-3-one, but the principal product is the hemiperketal from the 5-alpha-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. 3-beta-Benzoyloxy-5-alpha-tributylstannylperoxycholest-6-ene undergoes the Schenck and Smith types of rearrangement by a radical chain mechanism to give successively the corresponding 7-alpha- and 7-beta-stannylperoxy-5-enes.