ChemInform Abstract: An Efficient Synthesis of (Z)-γ-Fluoroallylphosphonates Using a Base-Promoted Deconjugation of (E)-γ-Fluorovinylphosphonates, and Its Utility as Fluoroolefin-Containing Building Block.

Abstract

Abstract A three-step synthesis of γ-fluoroallylphosphonates starting with α,β-unsaturated aldehydes is described. Treatment with diethyl phosphite in the presence of KF gives α-hydroxyallyl phosphonate in excellent yield; DAST deoxofluorination produces the corresponding γ-fluorovinylphosphonate through a S N 2′ mechanism, and finally, a base-promoted double bond migration leads to the desired γ-fluoroallylphosphonate. γ-Fluoroallylphosphonate is a useful building block in the synthesis of fluoroolefins. An exploratory study yielded excellent yields of ( Z )-diethyl 1-benzyl-3-fluoro-2-butenylphosphonate and ( Z )-diethyl 1,3-difluoro-2-hexenylphosphonate. Treatment of ( E )-diethyl 3-fluoro-2-hexenylphosphonate with LiN(TMS) 2 and benzaldehyde in THF led to the preferential formation of syn -( Z )-diethyl 3-fluoro-1-(hydroxybenzyl)-2-butenylphosphonate.