A metal-free synthesis of aryltriphenylphosphonium bromides by the reaction of triphenylphosphine with aryl bromides in refluxing phenol is developed. This reaction tolerates hydroxymethyl, hydroxyphenyl, and carboxyl groups in aryl bromides, allowing to synthesize multifunctional aryltriphenylphosphonium bromides, from which facile access to multifunctional aryldiphenylphosphines and their oxides by hydrolysis and subsequent reduction is exemplified. A two-step addition–elimination mechanism, with the elimination step being a fast step, is also proposed.

A two-step method for the synthesis of aryldiphenylphosphine oxides from tertiary diphenylphosphines and aryl bromides is developed. The first step is the quaternization of methyldiphenylphosphine or benzyldiphenylphosphine with aryl bromides. This quaternization can be nickel-catalyzed (metal-free in some cases), and tolerate of a variety of functional groups, furnishing quaternary phosphonium salts in 48−90% yields. The second step is Wittig reactions of these quaternary phosphonium salts with furan-2-carbaldehyde or p-chlorobenzaldehyde to provide aryldiphenylphosphine oxides in 27−90% yields. The use of the Wittig reaction for the synthesis of tertiary phosphine oxides is in contrast to its traditional use for the synthesis of olefins, leaving tertiary phosphine oxide as a byproduct. This quaternization−Wittig method can be applied to synthesize aryldiphenylphosphine oxides that are difficult to access by the alkaline hydrolysis of aryltriphenylphosphonium salts, especially those bearing an electron-deficient aryl group. The ligand-coupling mechanism for the alkaline hydrolysis of (p-acylphenyl)triphenylphosphonim salts is also discussed.

H and 13 C NMR spectra were recorded on a Bruker Avance 400 NMR spectrometer. HRMS spectra were recorded on a Varian 7.0 T FTMS. The 1 M solution of t-BuOK in THF and THF (SuperDry) were purchased from a local company. The preparation of phosphonium salts 1b, 1d, and 1f has been reported in our previous paper. 1 The same procedure was used for the preparation of phosphonium salt 1a. Phosphonium salts 1c, 1e, and 1g were prepared by the same procedure except that a catalytic amount of NiBr2 was added. Phosphonium salts 1h and 1i as well as ylides 4 and 5 were purchased from a local company.(4-Acetylphenyl)triphenylphosphonium bromide (1a) 2