N‐acylation of 1,3‐dimethyl‐6‐aminouracils. A reversal in the regiospecificity of an electrophilic substitution induced by an intramolecular proton‐transfer

Electrophilic reactions of 1,3‐dimethyl‐6‐aminouracil lead to 5‐substituted derivatives. The introduction of a dialkylaminoalkylamino chain in the 6‐position of 1,3‐dimethyluracil modifies the regiospecificity of the acylation reaction to give N‐6 acylated compounds. This reversal in acylation is induced by an intramolecular proton‐transfer which introduces a change in the electron density of the enamine system. The cyclic transition state and the spatial conformation of the final products substantiate the proposed mechanism, on the basis of X‐ray and 1 H nmr data.