Synthesis of novel phosphonium betaines and bis-betaines derived from hexafluoro-1,4-naphthoquinone

Abstract

Reactions of hexafluoro-1,4-naphthoquinone with phosphorus-centered bis-phenylphosphanes with structure Ph2P(CH2)nPPh2 (where n=1–5) and Et2P(CH2)2PEt2 in various solvents (anhydrousC6H6, aq. C6H6, aq. dioxane, aq. DMSO, or MeOH) were investigated. It was shown that the use of aqueous dioxane and DMSO leads to target products of phosphanodefluorination (i.e., phosphorus-containing betaines and bis-betaines) with high yields. We found that the betaines upon purification by thin-layer chromatography underwent various transformations such as a ring contraction (thus yielding novel polyfluorinated indenones) or addition of an acetone molecule at the CO bond of the fluorinated 1,4-naphthoquinone. According to X-ray diffraction analysis, there were intermolecular F⋯π interactions in the crystal packing of all the obtained betaines. The interactions are characterized by short distances F⋯Cg from 3.151(5) to 3.831(2) Å (where Cg is a centroid of π-system).