Anti-Markovnikov hydroimination of terminal alkynes in gold-catalyzed pyridine construction from ammonia

Glutaconaldehyde as an Alternative Reagent to the Zincke Salt for the Transformation of Primary Amines into Pyridinium Salts

In the presence of amines, the degradation of glutaconaldehyde in acidic medium can be prevented. By exploitation of this behavior, primary amines are transformed into their corresponding pyridinium salts, including those substrates that remain unreactive toward the Zincke salt, which is the reagent typically used to perform this transformation. The use of glutaconaldehyde also allows control of the nature of the counterion of the pyridinium with no need for additional salt metathesis reaction.

The pyrrole ring η2-hapticity bridged binuclear tricarbonyl Mo(0) and W(0) complexes: catalysis of regioselective hydroamination reactions and DFT calculations

Following the report of the ferrocene structure, metal complexes containing the heteroatom-substituted cyclopentadienyl (Cp) analogue, that is the η⁵ pyrrolyl ligand, have been reported. While the Cp ligand continues to be a favorite ligand in organometallics, the transition metal chemistry of the pyrrolyl ligand is still in the developing stage. In view of this, we carried out the reaction between the multidentate ligand 2,3,4,5-tetrakis(3,5-dimethylpyrazolylmethyl)pyrrole (LH) and Mo(CO)₆ or [W(CO)₃(CH₃CN)₃] and isolated two new binuclear tricarbonyl Mo(0) and W(0) complexes, [Mo₂(CO)₆(μ-η²:η²-LH-κ⁴N)] (1) and [W₂(CO)₆(μ-η²:η²-LH-κ⁴N)] (2). Their X-ray structural analyses showed that the metal centers are bridged by the double bonds of the central pyrrole ring (μ-η²:η²), a rarely observed coordination mode. Interestingly, complex 1 is a catalyst precursor for the hydroamination reactions of phenylacetylene with a series of secondary amines at room temperature offering the regioselectively formed anti-Markovnikov product in excellent yields. In addition, DFT calculations were performed to understand the bonding nature of the pyrrole ring in 1 and 2 and to estimate the energy of six different conformations of LH.

Pyridylidene ligand facilitates gold-catalyzed oxidative C-H arylation of heterocycles

Triaryl-2-pyridylidene effectively facilitates the gold-catalyzed oxidative C-H arylation of heteroarenes with arylsilanes as a unique electron-donating ligand on gold. The employment of the 2-pyridylidene ligand, which is one of the strongest electron-donating N-heterocyclic carbenes, resulted in the rate acceleration of the C-H arylation reaction of heterocycles over conventional ligands such as triphenylphosphine and a classical N-heterocyclic carbene. In situ observation and isolation of the 2-pyridylidene-gold(III) species, as well as a DFT study, indicated unusual stability of gold(III) species stabilized by strong electron donation from the 2-pyridylidene ligand. Thus, the gold(I)-to-gold(III) oxidation process is thought to be facilitated by the highly electron-donating 2-pyridylidene ligand.

Copper-Mediated Cross-Dehydrogenative Coupling of 2-Methylpyridine and 8-Methylquinoline with Methyl Ketones and Benzamides

A synthetic method to prepare (E)-(pyridin-2-yl)enones and (E)-(quinolin-8-yl)enones that relies on the respective copper(I)-catalyzed formal cross-dehydrogenative coupling (CDC) reaction of 2-methylpyridine and 8-methylquinoline with methyl ketones has been discovered. The mechanism was delineated to follow a pathway involving oxidation of the N-heterocycle to its corresponding aldehyde adduct prior to reaction with the methyl ketone. The versatility and substrate dependent divergence in the reactivity of the copper-mediated CDC strategy was exemplified by its application to the synthesis of N-(quinolin-8-ylmethyl)amide and N-(quinolin-8-ylmethyl)aniline adducts on switching the cross-coupling partner to benzamides or an aniline derivative.