Collect. Czech. Chem. Commun. 1980, 45, 3199-3209

Participation of 19-substituents in acid cleavage of steroidal 3α,4α- and 4α,5α-epoxides

Pavel Kočovský and Václav Černý

Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6


Participation of the 19-methoxy and 19-acetoxy group in 3α,4α- and 4α,5α-epoxides IIIc, IVb,c on treatment with aqueous perchloric or hydrobromic acid is investigated and compared with acid treatment of structurally similar 19-substituted 6α,7α- and 5α,6α-epoxides V and VI and with the behavior of analogous 3α,4α- and 4α,5α-bromonium ions. The 3α,4α-epoxides III react readily with 5(O)n participation. The reaction is practically quantitative on perchloric acid treatment. Under the same conditions, the 19-methoxy-4α,5α-epoxide IVb suffers mainly external attack leading to the diol XIb. The neighboring group participation is solely a 5(O)n process giving rise to the cyclic ether X. The 19-acetoxy-4α,5α-epoxide IVc reacts predominantly with participation of the ambident acetoxy group. This reaction is exclusively a 6(O)π,n process affording the diol XVI. External attack proceeds to a limited extent to give the isomeric diol XIc. In this respect the latter compounds react quite analogously to 5α,6α-epoxides VI and 4α,5α- and 5α,6α-bromonium ions bearing 19-acetoxyl.