An unusual oxidative transformation of alpha,beta-unsaturated gamma-la
ctone of the cardenolide gitoxin (1a) by tetra-n-butylammonium fluorid
e (TBAF) is reported. The structure of the product (2a) was finally co
nfirmed by an X-ray crystal structure analysis of its genin (2b). The
oxidation proceeded also in the presence of CsF, and KF + 18-crown-6.