The anionic polymerization of methylidene malonate 2.1.2. is able to yield four different molecule types. The major product obtained at pH 5.5 corresponds to a trisubstituted cyclohexanone formed by a back-biting reaction. A mixture of four diastereoisomer couples due to the presence of three asymmetric carbon atoms was produced in the same proportion. These results were deduced from mass spectrometry (MS), liquid chromatography-MS (LC-MS) and 1 H nuclear magnetic resonance (NMR) investigations.