Catalyst‐Free Visible Light Mediated Synthesis of Unsymmetrical Tertiary Arylphosphines

Abstract

Arylation of tertiary aryl and alkyl phosphines bearing 2-cyanoethyl group with aryl(mesityl)iodonium triflates under blue light irradiation followed by retro-Michael reaction of the in situ generated quaternary phosphonium salts initiated by DBU represent a novel efficient and general method for the preparation of distinctly substituted tertiary arylphosphines. An operationally simple, one-pot protocol features mild, transitionmetal-free conditions, high selectivity, broad functional group compatibility, as well as scalability and would be applied to substrates with different electronic and steric nature.

Electron Donor‐Acceptor Complex Initiated Photochemical Phosphorus Arylation with Diaryliodonium Salts toward the Synthesis of Phosphine Oxides

“…In general, the transition metal-free arylation with diaryliodonium salts proceeds either via a concerted ligand coupling or a SET (single electron transfer) mechanisms. [23] Considering our previous reports 5,6 and the literature precedence, [4d,7-9,24] it is most likely that the formation of the CÀ P-bond in our protocol proceeds through a coupling of carbon-and phosphorcentered radicals generated by a photochemically induced SET in the EDA complex initially formed between diaryliodonium salt 1 and aminophosphine 2. Owing to two vacant orbitals at the iodine atom, diaryliodonium cations act as halogen bond donors generating noncovalent interactions with Lewis bases (halogen bonding).…”

“…Owing to two vacant orbitals at the iodine atom, diaryliodonium cations act as halogen bond donors generating noncovalent interactions with Lewis bases (halogen bonding) [25] . In most cases, however, the resultant EDA complexes are difficult to observe by spectroscopic methods due to weak interaction of diaryliodonium salts with P (III) compounds [5–7,26] …”

“…Recently our group reported on the electron donor acceptor complex initiated photochemical arylation of a tertiary P-atom with diaryliodonium salts for the synthesis of quaternary phosphonium salts [5] and tertiary aryl phosphines. [6] It was not long before, the Lakhdar group employed the same methodology for the visible light-promoted synthesis of aryl phosphonates from diaryliodonium salts and phosphites under photoredox catalyst free conditions. [7] Similarly, the EDA complex-based strategy was used for phosphonation of aryl halides under visible [8] or UV [9] light irradiation.…”

“…[25] In most cases, however, the resultant EDA complexes are difficult to observe by spectroscopic methods due to weak interaction of diaryliodonium salts with P (III) compounds. [5][6][7]26] To verify the formation of the EDA complex between reagents in our reaction we performed several spectroscopic experiments using (4-ethoxycarbonylphenyl)(mesityl)iodonium triflate (1 t) and bis(diethylamino)(o-tolyl)phosphine (2 d) as model acceptor and donor respectively. First, after mixing of the above reagents in MeCN a light-yellow color was developed within minutes, indicating a plausible new molecular aggregation, a colored EDA complex in the ground states (Figure 1A).…”

A General Electron Donor–Acceptor Photoactivation Platform of Diaryliodonium Reagents: Arylation of Heterocycles

“…Although there are beautiful examples on EDA formation with DAIRs, applications of an EDA strategy involving DAIRs in the arylation of heterocycles are largely unexplored. − , To the best of our knowledge, there is only a single report where electron-rich pyrroles form an EDA with DAIRs and provide the corresponding products in moderate yields . Unfortunately, this approach is strictly limited to electron-rich heteroarenes and may not be applicable to a broad range of heterocycles, especially electron-deficient congeners.…”