a-Chloro-N-arylisobutyrimidyl chloride (I) reacted with ethyl sodiomalonate to afford N-aryl-2,2-dimethyl-3 carbethoxysuccinimide. This reaction seems to proceed in a different mechanism from that of the synthesis of tetronic acids(2) and is supposed to involve a primary attack of the carbanion at the a-carbon atom of the chloride followed by the cyclization.