Collect. Czech. Chem. Commun. 1979, 44, 1483-1495

Participation of 19-ester groups in hypobromous acid additions to 2,3- and 5,6-unsaturated steroids

Pavel Kočovský, Václav Černý and Miroslava Synáčková

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


Hypobromous acid action upon the 2,3-unsaturated acetoxy derivative Ia results in the formation of two products, the bromohydrin IVa and the cyclic ether VI as a product of the participation of ether oxygen of the ester group. Both these compounds are formed from the 2α,3α-bromonium ion XIIIa. Under the same conditions the 5,6-unsaturated 19-acetoxy derivative IIa afforded a mixture of the following products: Bromohydrin Xa as the product of a normal reaction course and the isomeric bromohydrin VIIa arising by intramolecular interaction with the carbonyl oxygen of the 19-acetoxy group. Both these compounds are formed from the 5α,6α-bromonium ion XVIIIa. The epimeric 5β,6β-bromonium ion XVIIa gives rise to the bromohydrin XIa. The mechanism of these reactions, difference in behavior of both olefins I and II and the competition between ambident neighboring group participation and external nucleophile attack is discussed.