New insights into the chemistry of gem-bis(phosphonates): Unexpected rearrangement of Michael-type acceptors

Abstract

The 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 an attempt to explain the mechanisms involved. To the best of our knowledge, this reaction constitutes a remarkable novelty, being the first reported rearrangement reaction of an epoxy derivative of a gem-bis(phosphonate). In addition, evidence supporting the involvement of a radical or a polar mechanism, depending on the nature of the nucleophile, is discussed.