Keywords: Bis(phosphonic acids) / Michael additions / Radical mechanism / Polar mechanismThe use of tetraethyl ethylidenebis(phosphonate) as a Michael acceptor with different nucleophiles was investigated. It was found that in some cases this compound undergoes phosphate removal, depending on the nature of the nucleophile. The chemical behavior of its epoxy derivative tetraethyl oxiranylidenebis(phosphonate) as an electrophile was also studied. This compound underwent a very attractive and remarkable phosphonate-phosphate rearrangement resulting in the enol phosphate 8 regardless of the nucleophile employed. Different mechanistic studies were conducted in