Synthesis of α-fluoro-β,γ-alkenylphosphonates and conjugated fluoroenynes from a common intermediate (α-fluoropropargyl)phosphonate

The efficient preparation of alpha-fluoro-beta,gamma-alkenylphosphonate 3, via catalytic hydrogenation of (alpha-fluoropropargyl)phosphonate ester 1, is described. Conjugated fluoroenynes 4 have been synthesized using a modified Horner Wadsworth Emmons (HWE) olefination of aldehydes or ketones and 1 in relatively good yields. Yields were lowered because of the formation of alpha-fluoro-gamma-hydroxyallenylphosphonate 5 during the reaction. The nature of the counterion was very important in the outcome of the HWE reaction; better yields of fluoroenynes were obtained when a potassium base was used instead of a lithium base. (C) 1998 Elsevier Science Ltd. All rights reserved.