Insertion of nitriles into zirconocene 1-aza-1,3-diene complexes: chemoselective synthesis of N-H and N-substituted pyrroles

Catalysts-Controlled Roles Exchange between 2,3-Diaryl-2H-azirines and Acetone: Chemodivergent Synthesis of Pyrroles and 3-Oxazolines

We report two practical and step-economical methodologies for the chemodivergent synthesis of tri-substituted pyrroles and 3-oxazolines from the domino reactions of 2H-azirines and acetone. For instance, acetone served as a nucleophile to react with 2H-azirines under the basic conditions to furnish pyrroles. Upon changing the catalyst to TfOH, acetone served as an electrophile to synthesize 3-oxazolines. Moreover, the products could be synthesized on a gram scale, and the possible catalytic cycles were proposed.

Iron(0) tricarbonyl η4-1-azadiene complexes and their catalytic performance in the hydroboration of ketones, aldehydes and aldimines via a non-iron hydride pathway

Six iron(0) tricarbonyl complexes (1a-f) with a η⁴-1-azadiene moiety were prepared and their performance in the hydroboration of unsaturated organic compounds was investigated. All the complexes exhibit catalytic activity towards hydroboration of ketones, aldehydes and aldimines with pinacolborane (HBpin) as a hydride source to lead to secondary alcohols, primary alcohols, and secondary amines, respectively, after hydrolysis of the hydroboration products. Of the iron(0) tricarbonyl complexes, complex 1e is the most robust one and was employed throughout the catalytic investigation. Its preference towards the three types of substrates is as follows: aldimines > aldehydes ≫ ketones. In total, 24 substrates were examined for the catalytic hydroboration reactivity and generally, isolation yields ranging from 40% to 95% were achieved. Mechanistic investigation suggests that the catalytic hydroboration of the substrates proceeds via intramolecular hydride transfer without going through an Fe-H intermediate. As indicated by ¹H NMR spectroscopic monitoring, the substrates and the borane agent bind to the iron centre and the imine N atom, respectively, which facilitates the hydride transfer by activating the B-H bond and polarizing the double bond of the substrates.

Zirconium-Catalyzed Hydroalumination of C═O Bonds: Site-Selective De-O-acetylation of Peracetylated Compounds and Mechanistic Insights

An unprecedented hydroalumination of C ═ O bonds catalyzed by zirconocene dichloride is reported herein and applied to the site-selective deprotection of peracetylated functional substrates. A mixed metal hydride, with 1:1 zirconium/aluminum stoichiometry, is also shown to be the reductive species. A catalytic cycle is finally proposed for this transformation with no precedent in the field of zirconium catalysis.

Mechanistic insights into dehydrocoupling of amine boranes using dinuclear zirconocene complexes

Catalytic dehydrocoupling of H₃B·NMe₂H using Cp₂Zr(Cl)(μ-Me₃SiC₃SiMe₃)Zr(Cl)Cp₂ (1)/MeLi was studied. Spectroscopic monitoring and stoichiometric experiments show the formation and interconversion of several catalytically active Zr species.

Cu(i)- and Au(i)-catalyzed regioselective oxidation of diynes: divergent synthesis of N-heterocycles

The efficient and divergent construction of two types of valuable N-heterocycle is achieved easily, with the first example of the generation of α-oxo copper carbenes via copper-catalyzed oxidation of non-polarized alkynes.

Chemodivergent synthesis of multi-substituted/fused pyrroles via copper-catalyzed carbene cascade reaction of propargyl α-iminodiazoacetates

A novel cascade reaction of alkynyl-tethered α-iminodiazoacetates has been developed, which provides a general access to both multi-substituted and fused pyrroles in high yields with a broad substrate scope. The γ-imino carbene is proposed as the key intermediate in this divergent reaction and followed by unpresented transformations.

Copper/amine-catalyzed formal regioselective [3 + 2] cycloaddition of an α,β-unsaturated O-acetyl oxime with enals

A novel copper/amine co-catalyzed formal regioselective [3 + 2] cycloaddition reaction of an O-acyl oxime with α,β-unsaturated aldehydes is developed.

Plasma-Triggered CH4/NH3 Coupling Reaction for Direct Synthesis of Liquid Nitrogen-Containing Organic Chemicals

Nitrogen-containing organic chemicals such as amines, amides, nitriles, and hydrazones are crucial in chemical and medical industries. This paper reports a direct synthesis of N,N-dimethyl cyanamide [(CH₃)₂NCN] and amino acetonitrile (NH₂CH₂CN) through a methane/ammonia (CH₄/NH₃) coupling reaction triggered by dielectric barrier discharge plasma, with by-products of hydrazine, amines, and hydrazones. The influence of CH₄/NH₃ molar ratio, feedstock residence time, and specific energy input on the CH₄/NH₃ plasma coupling reaction has been investigated and discussed. Under the optimized conditions, the productivities of (CH₃)₂NCN and NH₂CH₂CN reached 0.46 and 0.82 g·L^-1·h^-1, respectively, with 8.83% CH₄ conversion. In addition, through combining the optical emission spectra diagnosis and the reaction results, a possible CH₄/NH₃ plasma coupling reaction mechanism has been proposed. This paper provides a potential fine application of CH₄ and NH₃ in green synthesis of liquid nitrogen-containing organic chemicals, such as nitriles, amines, amides, and hydrazones.

Catalytic formal [2+2+1] synthesis of pyrroles from alkynes and diazenes via Ti(II)/Ti(IV) redox catalysis

Pyrroles are structurally important heterocycles. However, the synthesis of polysubstituted pyrroles is often challenging. Here, we report a multicomponent, Ti-catalysed formal [2+2+1] reaction of alkynes and diazenes for the oxidative synthesis of penta- and trisubstituted pyrroles: a nitrenoid analogue to classical Pauson-Khand-type syntheses of cyclopentenones. Given the scarcity of early transition-metal redox catalysis, preliminary mechanistic studies are presented. Initial stoichiometric and kinetic studies indicate that the mechanism of this reaction proceeds through a formally Ti(II)/Ti(IV) redox catalytic cycle, in which an azatitanacyclobutene intermediate, resulting from [2+2] alkyne + Ti imido coupling, undergoes a second alkyne insertion followed by reductive elimination to yield pyrrole and a Ti(II) species. The key component for catalytic turnover is the reoxidation of the Ti(II) species to a Ti(IV) imido via the disproportionation of an η(2)-diazene-Ti(II) complex.