Synthesis of α- and γ-fluoroalkylphosphonates

Abstract

α-Fluorobenzylphosphonate esters are conveniently made by treating α-hydroxybenzylphosphonate esters with diethylaminosulphur trifluoride. The reaction is not subject to steric impedance and is extended to the α-fluorination of an α-hydroxybenzylphosphine oxide. For α-hydroxyallyl and α-hydroxycinnamylphosphonates, the replacement of the hydroxy group by fluorine proceeds via an S_N2′ rearrangement to give the γ-fluoroalk-1-enylphosphonates exclusively. Dehydration rather than substitution occurs in the case of alcohols of secondary alkylphosphonates.