Anionotropic and Prototropic Changes in the α-Bromo-ββ-dimethylacrylic Acid System

Abstract

IT has already been shown by one of us¹ that treatment of α-bromo-ββ-dimethylacrylic acid (I) with sodium alkoxides in the corresponding alcoholic solution gives a mixture of α-alkoxy-ββ-dimethylacrylic acid (IV) and α-alkoxy-β-methylenebutyric acid (III), with the latter preponderating. As a result of more detailed investigations it has now become clear that the 'normal' product (IV) is actually formed by a prototropic change from (III, since the relative proportion of (IV) to (III) increases with the duration of the reaction ; furthermore, the former can be prepared in excellent yield from the latter by warming with aqueous alkali. The formation of (III) can be explained by an initial prototropic rearrangement of the bromo-acid (I) into α-bromo-β-methylenebutyric acid (II), followed by nucleophilic replacement of bromine by alkoxyl ; the reactivity of the bromine atom, which in the original compound would be expected to be non-reactive, is thus understandable.