Metal-Free Synthesis of Aryltriphenylphosphonium Bromides by the Reaction of Triphenylphosphine with Aryl Bromides in Refluxing Phenol

Abstract

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.

Versatile Visible‐Light‐Driven Synthesis of Asymmetrical Phosphines and Phosphonium Salts

“…Asymmetrical quaternary phosphoniums alts (II, IV,s ee Figure2)a re mostlys ynthesized from tertiaryp hosphines through nucleophilic attack on alkyl or aryl (pseudo) halides and transition metal catalyzed (Pd, Ni)a rylation using haloarenes at (very) high temperatures (> 140 8C; Figure1c), [12] althoughasmall number of metal-free reactions have also been reported. [13] One of these involves the trapping of in situ generated arynes by tertiary phosphines but provideso nly poor regioselectivity. [13a] Another recently developed reactiono f PPh 3 with bromoarenes in phenol requires very high tempera-ture (180 8C).…”

“…One of these involves the trapping of in situ generated arynes by tertiary phosphines but provides only poor regioselectivity [13a] . Another recently developed reaction of PPh 3 with bromoarenes in phenol requires very high temperature (180 °C) [13b] . Alternatively, visible light‐driven reactions with iodonium salts have been reported, either mediated by a Ru‐based photosensitizer, [14] or using a metal free protocol facilitated by the formation of an electron donor‐acceptor complex formed from iodonium salts and tertiary phosphines (Figure 1 d).…”

Cationic Organophosphorus Chromophores: A Diamond in the Rough among Ionic Dyes

“…A facile metal catalyst‐free method to obtain phosphonium salts from oligophenylene and polyaromatic bromides is their coupling with triphenylphosphine in refluxing phenol (e.g. 1 a – f , Figure 1), [17] which allows for the utilization of functionalized precursors containing hydroxyl, ether/ester, carboxyl, and N ‐unsubstituted indolyl groups.…”

Unveiling Extreme Photoreduction Potentials of Donor-Acceptor Cyanoarenes to Access Aryl Radicals from Aryl Chlorides

“…Borylated derivatives of loratadine (34), meclizine (35), indomethacin (36), carbinoxamine (37), chloropyramine (38), cloperastine (39), chlorpromazine (40), and clofibrate (41) were generated in moderate to good yields. Some of the borylation products were isolated as organotrifluoroborate salts as a part of the workup procedure to assist product isolation.…”

“…37 However, existing methods for the preparation of arylphosphonium salts from aryl halides or pseudohalides rely on transition metal catalysis and high-temperature processes. 38 We herein developed a metal-free synthesis of arylphosphonium salts under ambient conditions using 3CzEPAIPN as the photocatalyst and substoichiometric DIPEA as the electron donor (Figure 2A). Notably, this reactivity enabled engagement of both electron-rich and electronpoor aryl chlorides (42-51), as well as various arylphosphines (52-54), delivering the desired phosphonium salts in good to excellent yields.…”