Palladium-catalyzed reaction of aryl iodides with acetic anhydride. A carbon monoxide-free synthesis of acetophenones

[reaction: see text] The palladium-catalyzed reaction of aryl iodides with acetic anhydride provides a straightforward and experimentally simple carbon monoxide-free route to acetophenones. The reaction tolerates a wide range of functionalized aryl iodides. Acetophenones are isolated in excellent yield with a variety of neutral, slightly electron-rich, and slightly electron-poor aryl iodides, whereas moderate yields are obtained with aryl iodides containing strongly electron-withdrawing substituents.     

Palladium-Catalyzed [2+2+1] Spiroannulation via Alkyne-Directed Remote C−H Arylation and Subsequent Arene Dearomatization

Palladium-catalyzed alkene-directed cross-coupling of aryl iodide with another aryl halide through C−H arylation opens a unique avenue for unsymmetrical biaryl-derived molecules. However, homo-coupling of aryl iodides often erodes the overall synthetic efficiency. Reported herein is a highly chemoselective Pd⁰-catalyzed alkyne-directed cross-coupling of aryl iodides with bromophenols, which was subsequently followed by phenol dearomatization to furnish a very attractive [2+2+1] spiroannulation. Notably, possible homo-coupling of aryl iodides was not observed at all. Mechanistic studies indicated that a five-membered aryl/vinyl palladacycle most likely accounts for promoting the key step of biaryl cross-coupling.     

Manganese‐Catalyzed Cross‐Coupling of Thiols with Aryl Iodides

A manganese‐catalyzed cross‐coupling reaction of thiols with aryl iodides, furnishing aryl thioethers in good to excellent yields has been reported; the system shows good functional group tolerance and enables the sterically demanding aryl iodides to couple with thiols.     

Palladium‐Catalyzed [2+2+1] Spiroannulation via Alkyne‐Directed Remote C−H Arylation and Subsequent Arene Dearomatization

Palladium‐catalyzed alkene‐directed cross‐coupling of aryl iodide with another aryl halide through C?H arylation opens a unique avenue for unsymmetrical biaryl‐derived molecules. However, homo‐coupling of aryl iodides often erodes the overall synthetic efficiency. Reported herein is a highly chemoselective Pd⁰‐catalyzed alkyne‐directed cross‐coupling of aryl iodides with bromophenols, which was subsequently followed by phenol dearomatization to furnish a very attractive [2+2+1] spiroannulation. Notably, possible homo‐coupling of aryl iodides was not observed at all. Mechanistic studies indicated that a five‐membered aryl/vinyl palladacycle most likely accounts for promoting the key step of biaryl cross‐coupling.     

Synthesis of symmetrical and unsymmetrical N,N'-diaryl guanidines via copper/N-methylglycine-catalyzed arylation of guanidine nitrate

CuI/N-methylglycine-catalyzed coupling reaction of guanidine nitrate with both aryl iodides and bromides takes place at 70-100 °C, affording symmetrical N,N'-diaryl guanidines with good to excellent yields. Unsymmetrical N,N'-diaryl guanidines can be assembled via monoarylation of guanidine nitrate with aryl iodides bearing a strong electron-withdrawing group and subsequent coupling with another aryl iodide.     

A general rhodium-catalyzed cross-coupling reaction of thiols with aryl iodides

The general procedure for the rhodium-catalyzed cross-coupling of thiols with aryl iodides is described. The catalytic system consists of 5 mol % of [RhCl(cod)]₂ and 10 mol % of PPh₃ as a ligand. A variety of aryl iodides reacted with thiols, giving aryl thioethers in good to excellent yields. It is important to note that the deactivated aryl iodides such as 4-iodoanisole is worked smoothly to provide the corresponding aryl thioethers in excellent yields. Functional groups such as free-amines, chloro, are all tolerated under the employed reaction conditions.     

Palladium-catalyzed oxidative coupling of trialkylamines with aryl iodides leading to alkyl aryl ketones

A new, simple method for selectively synthesizing alkyl aryl ketones has been developed by palladium-catalyzed oxidative coupling of trialkylamines with aryl iodides. In the presence of PdCl(2)(MeCN)(2), TBAB, and ZnO, a variety of aryl iodides underwent an oxidative coupling reaction with tertiary amines and water to afford the corresponding alkyl aryl ketones in moderate to excellent yields. It is noteworthy that this method is the first example of using trialkylamines as the carbonyl sources for constructing alkyl aryl ketone skeletons.     

Synthesis of Aryldifluoroamides by Copper‐Catalyzed Cross‐Coupling

A copper‐catalyzed coupling of aryl, heteroaryl, and vinyl iodides with α‐silyldifluoroamides is reported. The reaction forms α,α‐difluoro‐α‐aryl amides from electron‐rich, electron‐poor, and sterically hindered aryl iodides in high yield and tolerates a variety of functional groups. The aryldifluoroamide products can be transformed further to provide access to a diverse array of difluoroalkylarenes, including compounds of potential biological interest.     

Development of a room temperature Hirao reaction

Arylphosphonates were prepared at 25 °C through the palladium-catalyzed coupling of aryl iodides with a silver phosphonate. A wide range of aryl iodides were successfully employed including phenolic substrates as well as those containing an ortho substituent.     

Mild ketone formation via Ni-catalyzed reductive coupling of unactivated alkyl halides with acid anhydrides

Ni-catalyzed ketone formation through mild reductive coupling of a diverse set of unactivated alkyl bromides and iodides with particularly aryl acid anhydrides was successfully developed using zinc as the terminal reductant. These conditions also allow direct coupling of alkyl iodides with aryl acids in the presence of Boc(2)O and MgCl(2).     

Tetrazole-1-acetic acid as a ligand for copper-catalyzed N-arylation of imidazoles with aryl iodides under mild conditions

Tetrazole-1-acetic acid was found to serve as a superior ligand for CuI-catalyzed N-arylation of imidazoles with aryl iodides under a low catalyst loading (5 mol% of CuI). A variety of aryl iodides could be aminated to provide the N-arylated products in good to excellent yields without the need of an inert atmosphere.     

Two-step, one-pot Ni-catalyzed neopentylglycolborylation and complementary Pd/Ni-catalyzed cross-coupling with aryl halides, mesylates, and tosylates

Two-step, one-pot neopentylglycolborylation of aryl iodides and bromides catalyzed by NiCl2(dppe) and NiCl2(dppp) is reported. Electron-rich and electron-deficient aryl neopentylglycolboronates were efficiently cross-coupled with aryl iodides, bromides, chlorides, mesylates, and tosylates by exploiting complementary Pd/Ni and Ni/Ni catalysis. The borylation route was further extended to a three-step, one-pot synthesis of biaryls via in situ Ni-catalyzed borylation and Pd-mediated cross-coupling.     

Convenient copper- and solvent-free Sonogashira-type alkynylation of aryl iodides and bromides using Pd EnCat™

A straightforward methodology is described for the copper- and solvent-free alkynylations of aryl iodides and bromides using 0.1-0.01 mol % of Pd as Pd EnCat™ 40 or TPP30. High yielding reactions can be achieved under aerobic conditions for a variety of activated and deactivated aryl iodides; a few examples with aryl bromides are also described. Microwave irradiation is able to enhance yields and rates of these reactions.     

Ligand free copper-catalyzed N-arylation of heteroarylamines

An efficient protocol for ligand-free Cu-catalyzed N-arylation of heteroarylamines has been developed. With the use of 1% CuI, a wide range of aryl iodides and bromides coupled with heteroarylamines to afford the corresponding products in high yields. Further, this protocol is particularly suitable for reactions of the most hindered aryl iodides with 2-aminopyridines.     

Studies on Pd/imidazolium salt protocols for aminations of aryl bromides and iodides using lithium hexamethyldisilazide (LHMDS)

The reactions of a range of secondary amines with aryl bromides and iodides have been performed using an in situ protocol involving palladium and imidazolium salts. Many of these reactions proceed at room temperature, providing a mild protocol for aminations of aryl iodides and bromides. Key to the success of this procedure is the use of lithium hexamethyldisilazide (LHMDS) as base.     

Amino acid promoted CuI-catalyzed C-N bond formation between aryl halides and amines or N-containing heterocycles

CuI-catalyzed coupling reaction of electron-deficient aryl iodides with aliphatic primary amines occurs at 40 degrees C under the promotion of N-methylglycine. Using l-proline as the promoter, coupling reaction of aryl iodides or aryl bromides with aliphatic primary amines, aliphatic cyclic secondary amines, or electron-rich primary arylamines proceeds at 60-90 degrees C; an intramolecular coupling reaction between aryl chloride and primary amine moieties gives indoline at 70 degrees C; coupling reaction of aryl iodides with indole, pyrrole, carbazole, imidazole, or pyrazole can be carried out at 75-90 degrees C; and coupling reaction of electron-deficient aryl bromides with imidazole or pyrazole occurs at 60-90 degrees C to provide the corresponding N-aryl products in good to excellent yields. In addition, N,N-dimethylglycine promotes the coupling reaction of electron-rich aryl bromides with imidazole or pyrazole to afford the corresponding N-aryl imidazoles or pyrazoles at 110 degrees C. The possible action of amino acids in these coupling reactions is discussed.     

NHC‐Pd complex‐catalyzed double carbonylation of aryl iodides with secondary amines to α‐keto amides

A series of palladium–NHC compounds were prepared and their catalytic activity in the double carbonylation of aryl iodides to synthesize α‐keto amides were examined. Palladium complexes bearing mixed NHC–phosphine exhibited high efficiency for the double carbonylation reaction. The effects of different solvents, base, temperature, carbon monoxide (CO), pressure, various amine and aryl iodides were investigated. Both electron‐rich and electron‐deficient aryl iodides afforded the corresponding substituted α‐keto amides in moderate to good yields. A possible mechanism was also proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

Formation of self-assembled monolayers of π-conjugated molecules on TiO2 surfaces by thermal grafting of aryl and benzyl halides

We demonstrate the formation of molecular monolayers of π-conjugated organic molecules on nanocrystalline TiO(2) surfaces through the thermal grafting of benzyl and aryl halides. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were used to characterize the reactivity of aryl and benzyl chlorides, bromides, and iodides with TiO(2) surfaces, along with controls consisting of nonhalogenated compounds. Our results show that benzyl and aryl halides follow a similar reactivity trend (I > Br > Cl > H). While the ability to graft benzyl halides is consistent with the well-known Williamson ether synthesis, the grafting of aryl halides has no similar precedent. The unique reactivity of the TiO(2) surface is demonstrated using nuclear magnetic resonance spectroscopy to compare the surface reactions with the liquid-phase interactions of benzyl and aryl iodides with tert-butanol and -butoxide anion. While the aryl iodides show no detectable reactivity with a tert-butanol/tert-butoxide mixture, they react with TiO(2) within 2 h at 50 °C. Atomic force microscopy studies show that grafting of 4-iodo-1-(trifluoromethyl)benzene onto the rutile TiO(2)(110) surface leads to a very uniform, homogeneous molecular layer with a thickness of ～0.45 nm, demonstrating formation of a self-terminating molecular monolayer. Thermal grafting of aryl iodides provides a facile route to link π-conjugated molecules to TiO(2) surfaces with the shortest possible linkage between the conjugated electron system and the TiO(2).     

Heck reactions of alkenes with aryl iodides and aryl bromides: Rate-determining steps deduced from a comparative kinetic study of competing and noncompeting reactions

Joint kinetic analysis of competition and noncompetition experiments can provide important information and sometimes a direct answer concerning the rate-determining step of a catalytic reaction. Applying this approach to the Heck reaction has demonstrated that alkenes; reactive aryl iodides; and, contrary to the conventional opinion, unactivated aryl bromides participate in rapid steps of the Heck reaction. For aryl iodides, the rate-determining step includes the dissociation of a C-H bond. At the same time, kinetic data for the dissolution of palladium reacting with aryl bromides suggest that the rate of the catalytic reaction is determined by the slow dissolution of palladium aggregates.