New Insights into the Chemistry of gem-Bisphosphonates: Unexpected Rearrangement of Michael-type Acceptors

SZAJNMAN, SERGIO HERNÁN; GARCÍA-LIÑARES, GUADALUPE; MORO, PABLO; RODRIGUEZ, JUAN BAUTISTA

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY

Wiley-VCH

Lugar: Weinheim; Año: 2005 p. 3687 - 3696

1434-193X

The use of tetraethyl ethenylidenebisphosphonate as a Michael acceptor with different nucleophiles was investigated. It was found that this compound undergoes phosphate removal in some cases depending on the nature of the nucleophile. Moreover, the chemical behavior of its epoxy derivative tetraethyl oxiranylidenebisphosphonate as an electrophile was studied. This compound experienced a very attractive and remarkable phosphonate-phosphate rearrangement that leads to the enol phosphate 8 regardless of the employed nucleophile. 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 report about a rearrangement reaction of an epoxy derivative of gem-bisphosphonates. In addition, evidence that supports involvement of a radical or a polar mechanism, depending of the nature of the nucleophile, is discussed.