Tetraethyl Vinylidenebisphosphonate: A Versatile Synthon for the Preparation of Bisphosphonates

Abstract

Tetraethyl vinylidenebisphosphonate is a versatile synthetic intermediate that allows access to a variety of highly functionalized compounds bearing the bisphosphonic moiety. As an electron-deficient alkene, this compound is able to undergo conjugate addition with a variety of reagents including strong nucleophiles, such as organometallic reagents and enolates, as well as very mild nucleophiles, such as amines, mercaptans and alcohols. The title compound also possesses the ability to behave as a dipolarophile or dienophile in 1,3-dipolar cycloadditions or Diels–Alder reactions, giving rise to five- or six-membered rings containing the bisphosphonic unit. In summary, tetraethyl vinylidenebisphosphonate is a very useful synthon to have at hand for straightforward syntheses of bisphosphonate derivatives of diverse structures. This bisphosphonate moiety has proven to be very important to impart important pharmacological action. 1 Introduction 2 General Reactivity 3 Michael Addition Reactions 3.1 Reaction with Organometallic Reagents 3.2 Reaction with Mercaptans and Amines 3.3 Reaction with Phosphorus-Containing Nucleophiles 3.4 Epoxidation, Loss of a Phosphonate Unit and Rearrangement Reactions 3.5 Michael Reactions with Enolates 4. Cycloaddition Reactions 4.1 Diels–Alder Reactions 4.2 1,3-Dipolar Cycloadditions 4.2.1 Reaction with Diazo Compounds 4.2.2 Reaction with Nitrones 4.2.3 Reaction with Nitrile Oxides 4.2.4 Grigg Azomethine Ylide Cyclizations 4.2.5 Reaction with Azides 5 Concluding Remarks