Hydrophosphorylation of 1,1,1,3,3,3-hexafluorobut-2-yne (HFB) with Diethyl Hydrogenphosphonate: Attractive Synthetic Route to Various Types of CF3-Containing Phosphonates

Abstract

The reaction of 1,1,1,3,3,3-hexafluorobut-2-yne (1) (HFB) with diethyl hydrogenphosphonate (2) was investigated under various conditions by promotion with transition metal catalysts, under heating without catalysts and by tert-amine catalysis. In all cases, double addition was the predominant reaction forming bis(phosphonic) acid esters 3, which were then converted to the corresponding acids 8 and salts 9. Compounds 3, 8, and 9 containing two chiral carbon atoms and three types of substituents exist as mixtures of diastereomers in the meso and dl forms, which can undergo epimerization. The mono adduct 4 was extremely unstable and capable of telomerization under rhodium complex catalysis or heating at 150 °C in catalyst free conditions. Isolated telomer 5 (n = 2) was characterized by X-ray crystallography and NMR method. Dephosphorylation of phosphonate 5 by Me₄NF occurred quantitatively to give, unexpectedly, internal salt of pyrrolidine 12 containing four trifluoromethyl substituents.