Oxygen nucleophiles as reaction partners in photoinduced, copper-catalyzed cross-couplings: O-arylations of phenols at room temperature

Abstract

Most copper-catalyzed cross-couplings require an elevated reaction temperature. Recently, a photoinduced variant has been developed that enables C-X bond-forming reactions of certain nitrogen and sulfur nucleophiles to proceed under unusually mild conditions (À40 C to room temperature). In view of the importance of carbon-oxygen bond construction in organic chemistry, the expansion of this photochemical approach to oxygen nucleophiles is an important objective. In this report, we establish that, in the presence of light and an inexpensive copper pre-catalyst (CuI), a wide array of phenols and aryl iodides can be coupled to generate diaryl ethers under mild conditions (room temperature) in the presence of a variety of functional groups. Our studies indicate that a Cu(I)-phenoxide complex is a viable intermediate in photoinduced C-O bond-formation.

Scalable, Metal- and Additive-Free, Photoinduced Borylation of Haloarenes and Quaternary Arylammonium Salts

“…Photoinduced Ar–X bond dissociation is a key step in a number of important photochemical carbon–carbon and carbon–heteroatom bond-forming reactions, including nucleophilic substitution, 20 arylation, 21 alkylation, 22 and photocyclization 23 reactions.…”

Copper-Catalyzed Alkylation of Aliphatic Amines Induced by Visible Light

“…With regard to the identity of the primary photoreductant, ESI–MS of a reaction mixture after partial conversion reveals the presence of copper(I)–binaphtholate complex E’ ; alternatively, deprotonated BINOL itself could also fill this role. 18,19 The illustrated mechanism includes d 9 copper(II) complexes as intermediates, and we have indeed detected such species via EPR spectroscopy by sampling a catalyzed coupling at partial conversion; at least two copper(II) species are evident (hyperfine coupling to copper), which together account for ~60% of the total copper that is present in the reaction mixture.…”

“…In earlier work, we have described a variety of coupling reactions of nucleophiles with organic (aryl, alkenyl, alkynyl, and alkyl) electrophiles that are induced by light and catalyzed by copper; 6,9 an outline of one of the possible pathways for such processes is provided in Figure 1. 10,11 To date, all of our reported couplings have employed nucleophiles wherein the nucleophilic site is part of a π system (N: carbazole, indole, and imidazole; S: aryl thiol; O: phenol; C: cyanide).…”

“…While examining the functional-group compatibility of a method that we had developed for photoinduced, copper-catalyzed arylations of phenols, 9d we discovered that the presence of 1.0 equiv of an aliphatic amine additive unexpectedly leads to predominant N-arylation of the aliphatic amine, rather than O-arylation of the phenol (eq 4; in the absence of n -BuNH 2 : 80% yield of PhO–Ar).…”

Additive- and Metal-Free, Predictably 1,2- and 1,3-Regioselective, Photoinduced Dual C–H/C–X Borylation of Haloarenes

“…Due to the combined radical and cationic character of these species, their reactivity is distinctively different from the reactivity of the ground state aryl cations and aryl radicals. 14 The multitude of reactivity patterns available after photoactivation of haloarenes has enabled a number of important carbon–heteroatom and carbon–carbon bond-forming reactions, including photoinduced nucleophilic substitution, 15 arylation, 16 alkylation, 17 and photocyclization 18 reactions.…”