Gold-Catalyzed Intermolecular, anti-Markovnikov Hydroarylation of Methylenecyclopropanes with Indoles

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

Kinetic studies on the intramolecular hydroamination of protected variants of 2,2-diphenylpent-4-en-1-amine were carried out under a variety of conditions with cationic gold catalysts supported by phosphine ligands. The impact of ligand on gold, protecting group on nitrogen, and solvent and additive on reaction rates was determined. The most effective reactions utilized more Lewis basic ureas, and more electron-withdrawing phosphines. A DCM/alcohol cooperative effect was quantified, and a continuum of isotope effects was measured with low KIE's in the absence of deuterated alcoholic solvent, increasing to large solvent KIE's when comparing reactions in pure MeOH to those in pure MeOH-d4. The effects are interpreted both within the context of a classic gold π-activation/protodeauration mechanism and a general acid-catalyzed mechanism without intermediate gold alkyls.

Catalytic Gold Chemistry: From Simple Salts to Complexes for Regioselective C-H Bond Functionalization

Gold coordinated to neutral phosphines (R₃ P), N-heterocyclic carbenes (NHCs) or anionic ligands is catalytically active in functionalizing various C-H bonds with high selectivity. The sterics/electronic nature of the studied C-H bond, oxidation state of gold and stereoelectronic capacity of the coordinated auxiliary ligand are some of the associated selectivity factors in gold-catalyzed C-H bond functionalization reactions. Hence, in this review a comprehensive update about the action of different types of gold catalysts, from simple to sophisticated ones, on C-H bond reactions and their regiochemical outcome is disclosed. This review also highlights the catalytic applications of Au(I)- and Au(III)-species in creating new opportunities for the regio- and site-selective activation of challenging C-H bonds. Finally, it also intends to stress the potential applications in selective C-H bond activation associated with a variety of heterocycles recently described in the literature.

Iron-Catalyzed Ortho C-H Homoallylation of Aromatic Ketones with Methylenecyclopropanes

We report here a C-H homoallylation reaction of aromatic ketones with methylenecyclopropanes (MCPs) only using a catalytic amount of Fe(PMe₃)₄. A variety of aromatic ketones and MCPs are applicable to the reaction to form ortho-homoallylated aromatic ketones selectively via regioselective scission of the three-membered rings. The homoallylated products are amenable to further elaborations, providing functionalized 1,2-dihydronaphthalenes.

[C^N]-Alkenyl Gold(III) Complexes by Proximal Ring-Opening of (2-Pyridyl)alkylidenecyclopropanes: Mechanistic Insights

Pyridine-substituted alkylidenecyclopropanes (Py-ACPs) react with gold(III) salts under mild reaction conditions through an unprecedented, proximal ring-opening pathway, to generate highly appealing, catalytically active pyridine alkenyl [C^N]-gold(III) species. Mechanistic studies reveal that the activation of the C-C bond of the ACP takes place through an unusual concerted, σ-bond metathesis type-process.

NHC/Nickel(II)-Catalyzed [3+2] Cross-Dimerization of Unactivated Olefins and Methylenecyclopropanes

Cross-dimerization of a methylenecyclopropane (1) and an unactivated alkene (2) with typical hydroalkenylation reactivity was observed for the first time by using a [NHC-Ni(allyl)]BAr^F catalyst (NHC=N-heterocyclic carbene). Results show that the C-C cleavage of 1 did not involve a Ni⁰ oxidative addition, which was crucial in former systems. Thus the method reported here emerges as a complementary method for attaining highly chemo- and regioselective synthesis of methylenecyclopentanes (3) with broad scope. An efficient NHC/Ni^II -catalyzed rearrangement of 1 leads to the convergent synthesis of 3 in the presence of 2.

In(OTf)3-catalyzed intramolecular hydroarylation of α-phenylallyl β-ketosulfones – synthesis of sulfonyl 1-benzosuberones and 1-tetralones

In(OTf)₃-catalyzed intramolecular hydroarylation of α-phenylallyl β-ketosulfones provides sulfonyl 1-benzosuberones and 1-tetralones in moderate to good yields in refluxing (CH₂Cl)₂ under open-vessel and easy-operation reaction conditions. A plausible mechanism is proposed and discussed. This highly regioselective protocol provides an atom-economic ring-closure route.

In(OTf)₃-catalyzed intramolecular hydroarylation of α-phenylallyl β-ketosulfones provides sulfonyl 1-benzosuberones and 1-tetralones in moderate to good yields in refluxing (CH₂Cl)₂ under open-vessel and easy-operation reaction conditions.

Azulenes with aryl substituents bearing pentafluorosulfanyl groups: synthesis, spectroscopic and halochromic properties

Azulenes with SF₅-containing substituents gave significantly different spectroscopic responses to protonation depending on the regioisomer in question.

Catalytic Functionalization of C-H Bonds of Azulene by Carbene/Nitrene Incorporation

The selective catalytic functionalization of the C-H bond of azulene upon incorporation of carbene or nitrene units with metal-based catalysts is described. Ethyl diazoacetate or ArI═NTs are employed as carbene or nitrene precursors, respectively. The azulene derivatives are subsequently employed as building blocks toward more complex structures with potential use as biodegradable materials.