Protoanemonin, reacts in different ways with thiolate and alkoxide anions. Thus, while the very soft nucleophile benzenethiolate attacks exclusively the olefinic carbons of 1, alkoxides always attack the carbonyl group in the first step of the reaction. In intermediate cases, when neither very hard nor very soft nucleophiles are used, regioselectivity is not observed. Mechanisms are discussed to explain this differential reactivity. © 1984.