Collect. Czech. Chem. Commun. 1982, 47, 124-129

Mechanism of acid cleavage of some steroid epoxides. Competition between neighboring group participation and external nucleophile attack

Pavel Kočovskýa, František Turečekb and Václav Černýa

a Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6
b Jaroslav Heyrovský Institute of Physical Chemistry and Electrochemistry, Czechoslovak Academy of Sciences, 121 38 Prague 2


The mechanism of perchloric acid cleavage of epoxides I and II was established on the basis of experiments using H2 18O. The 2α,3α-epoxide I gave two products: the cyclic ether V (60%) arising by 5(O)n participation of the 19-acetoxyl and the diol VI (40%). The latter compound is formed by two mechanisms: 1) By direct cleavage of the oxirane ring with H2 18O as external nucleophile and 2) by 7(O)π,n participation via the ion III. Under the same conditions the 5α,6α-epoxide II yielded two diols: The diequatorial diol VIII (96%) arising by 6(O)π,n participation and the diaxial diol IX which is again formed by both direct cleavage of the oxirane ring with H2 18O and by 7(O)π,n participation via the intermediate ion X. The competition of several mechanisms is discussed.