152,103 research outputs found
Nickel-Mediated Hydrogenolysis of CâO Bonds of Aryl Ethers: What Is the Source of the Hydrogen?
Mechanistic studies of the hydrogenolysis of aryl ethers by nickel were undertaken with (diphosphine)aryl methyl ethers. A Ni(0) complex containing Niâarene interactions adjacent to the arylâO bond was isolated. Heating led to arylâO bond activation and generation of a nickel aryl methoxide complex. Formal ÎČ-H elimination from this species produced a nickel aryl hydride which can undergo reductive elimination in the presence of formaldehyde to generate a carbon monoxide adduct of Ni(0). The reported complexes map out a plausible mechanism of aryl ether hydrogenolysis catalyzed by nickel. Investigations of a previously reported catalytic system using isotopically labeled substrates are consistent with the mechanism proposed in the stoichiometric system, involving ÎČ-H elimination from a nickel alkoxide rather than cleavage of the NiâO bond by H_2
Mechanistic and computational studies of oxidatively-induced aryl-CF3 bond formation at palladium
This article describes the rational design of 1st generation systems for oxidatively-induced Arylâ CF3 bond-forming reductive elimination from PdII. Treatment of (dtbpy)PdII(Aryl)(CF3) (dtbpy = di-tert-butylbipyridine) with NFTPT (N-fluoro-1,3,5-trimethylpyridium triflate) afforded the isolable PdIV intermediate (dtbpy)PdIV(Aryl)(CF3)(F)(OTf). Thermolysis of this complex at 80 °C resulted in ArylâCF3 bond-formation. Detailed experimental and computational mechanistic studies have been conducted to gain insights into the key reductive elimination step. Reductive elimination from this PdIV species proceeds via pre-equilibrium dissociation of TfOâ followed by ArylâCF3 coupling. DFT calculations reveal that the transition state for ArylâCF3 bond formation involves the CF3 acting as an electrophile with the Aryl ligand acting as a nucleophilic coupling partner. These mechanistic considerations along with DFT calculations have facilitated the design of a 2nd generation system utilizing the tmeda (N,N,Nâ,Nâ-tetramethylethylenediamine) ligand in place of dtbpy. The tmeda complexes undergo oxidative trifluoromethylation at room temperature
Direct Introduction of a Dimesitylboryl Group Using Base-Mediated Substitution of Aryl Halides with Silyldimesitylborane
The first dimesitylboryl substitution of aryl halides with a silylborane bearing a dimesitylboryl group in the presence of alkali-metal alkoxides is described. The reactions of aryl bromides or iodides with Ph2MeSi-BMes(2) and Na(OtBu) afforded the desired aryl dimesitylboranes in good to high yields and with high borylation/silylation ratios. Selective reaction of the sterically less-hindered C-Br bond of dibromoarenes provided monoborylated products. This reaction was used to rapidly construct a D-pi-A aryl dimesityl borane with a non-symmetrical biphenyl spacer
High throughput synthesis of 2,5-substituted indoles using a titanium carbenoid bearing boronate functionality
A titanium benzylidene complex bearing a boronate group converted resin-bound esters into enol ethers. Suzuki cross-coupling with aryl iodides followed by cleavage with acid completed the solid-phase synthesis of 2,5-disubstituted N-Boc-indoles. Also reported is the use of tert-butyllithium and 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane to convert an aryl bromide into an arylboronate in the presence of a dithiane, with simultaneous reduction of an aryl azide to an amine
Semiheterogeneous Dual Nickel/Photocatalytic (Thio)etherification Using Carbon Nitrides
A carbon nitride material can be combined with homogeneous nickel catalysts for light-mediated cross-couplings of aryl bromides with alcohols under mild conditions. The metal-free heterogeneous semiconductor is fully recyclable and couples a broad range of electron-poor aryl bromides with primary and secondary alcohols as well as water. The application for intramolecular reactions and the synthesis of active pharmaceutical ingredients was demonstrated. The catalytic protocol is applicable for the coupling of aryl iodides with thiols as well
Manganese carbonyl-mediated reactions of azabutadienes with phenylacetylene, methyl acrylate and other unsaturated molecules
Reaction of PhCHâMn(CO)â
with l,4-di-aryl-1-aza-1,3-butadienes gave substituted pyrrolinonyl rings which were ηâŽ-coordinated to a Mn(CO)â group. These are formed by intramolecular CO insertion into a (non-isolated) cyclomanganated intermediate, followed by cyclisation. Other unsaturated reagents (PhCâĄCH, CH2=CHCOOMe, PhNCO) gave products arising from insertion of these, including a structurally characterised tri-aryl-ηâ”-azacyclohexadienyl-Mn(CO)â complex from the reaction with the alkyne.
PhCHâMn(CO)â
reacts with l,4-di-aryl-1-aza-1,3-butadienes in the presence of unsaturated substrates to give products based on a cyclomanganated intermediate
Palladium-catalyzed acetylation of arenes.
A simple method for the preparation of aryl methyl ketones is reported. The transformation involves the Pd-catalyzed coupling of an acyl anion equivalent, acetyltrimethylsilane, with aryl bromides to afford the corresponding acetylated arenes in synthetically useful yields. The methodology is tolerant of heterocycles and provides a new method for arene functionalization
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