CuCl-catalyzed aerobic oxidation of 2,3-allenols to 1,2-allenic ketones with 1:1 combination of phenanthroline and bipyridine as ligands

Rh-Catalyzed Carbonylative Cyclization of Propargylic Alcohols with Aryl Boronic Acids

2(3H)-Furanones are tremendously important not only because of their wide occurrence in bioactive compounds but also due to their versatility in organic synthesis. Here, a straightforward approach to 2(3H)-furanones from readily available tertiary propargylic alcohols with arylboronic acids in the presence of CO using rhodium as a catalyst has been established. The method exhibits a broad substrate scope tolerating useful functional groups with a moderate to high stereoselectivity.

Cooperative Bimetallic Catalysis via One-Metal/Two-Ligands: Mechanistic Insights of Polyfluoroarylation-Allylation of Diazo Compounds

Metal/ligand in situ assembly is crucial for tailoring the reactivity & selectivity in transition metal catalysis. Cooperative catalysis via a single metal/two ligands is still underdeveloped, since it is rather challenging to harness the distinct reactivity profiles of the species generated by self-assembly of a single metal precursor with a mixture of different ligands. Herein, we report a catalytic system composed of a single metal/two ligands for a three-component reaction of polyfluoroarene, α-diazo ester, and allylic electrophile, leading to highly efficient construction of densely functionalized quaternary carbon centers, that are otherwise hardly accessible. Mechanistic studies suggest this reaction follows a cooperative bimetallic pathway via two catalysts with distinct reactivity profiles, which are assembled in situ from a single metal precursor and two ligands and work in concert to escort the transformation.

Ligand relay catalysis for cobalt-catalyzed sequential hydrosilylation and hydrohydrazidation of terminal alkynes

Sequential double hydrofunctionalizationalization of alkynes is a powerful method to construct useful vicinal compounds. Herein, we report a cobalt-catalyzed sequential hydrosilylation/hydrohydrazidation of alkynes to afford 1,2-N,Si compounds via ligand relay catalysis. A phenomenon of ligand relay is found that the tridentate anionic N-ligand (OPAQ) could capture the cobalt ion from bidentate neutral P-ligand (Xantphos) cobalt complex. This protocol uses three abundant chemical feedstocks, alkynes, silanes, and diazo compounds, and also features operationally simple, mild conditions, low catalyst loading (1 mol%), and excellent functional group tolerance. The 1,2-N,Si compounds can be easily further derivatized to afford various substituted silane derivatives via Si-H functionalization, alcohols via Fleming-Tamao oxidation, free amines and amides via N-N bond cleavage and protection. The asymmetric reaction could also be carried out to afford chiral products with up to 86% ee. The ligand relay has been supported by control experiments and absorption spectra.

In organic chemistry, performing sequential catalytic cycles with a single catalyst improves efficiency. Here the authors present a methodology to functionalize alkynes with nitrogen and silicon atoms, through two catalytic cycles with a homogeneous cobalt catalyst, which is bound to different ligands in each cycle.

Halogen-Substituted Allenyl Ketones through Ring Opening of Nonstrained Cycloalkanols

An efficient synthesis of halogen-substituted allenyl ketones via Ag-catalyzed oxidative ring opening of allenyl cyclic alcohols under mild reaction conditions has been achieved. The reaction features a wide substrate scope and excellent regioselectivity. The synthetic potential of the products has been demonstrated by their conversion to stereodefined alkenes and heterocyclic compounds.

Lewis Acid-Mediated Cyclization of Allenyl Aryl Ketones

The cyclization of a series of nonheterocyclic allenyl aryl ketones was examined using boron trifluoride etherate and indium triflate to mediate the reaction. Yields with BF₃ were low in most instances due mainly to competitive destruction of the substrates. With In(OTf)₃, there was less decomposition, and the yields of the cyclized product were much higher, but only for substrates with electron-donating substituents. Cyclization did not occur without those substituents. A computational study using the ωB97X-D/6-311+G(2d,p)//ωB97X-D/6-31+G(d,p) method confirmed better stability of the σ-complexed substrate by indium(III) and that meta-substituents on the phenyl ring of the substrate significantly influenced the activation barrier of the cyclization, whereas the effect of para-substituents was almost negligible. The computational results supported the idea that the cyclization is a 4π-electrocyclization and not a 5-endo-dig ring closure as had been proposed in the literature.

Copper catalysis for highly selective aerobic oxidation of alcohols to aldehydes/ketones

A general and practical room temperature aerobic oxidation of different types of alcohols using Cu(NO₃)₂·3H₂O and TEMPO or 4-HO-TEMPO as the catalysts forming aldehydes or ketones with an excellent selectivity has been developed.

Copper Catalysts for Aerobic Oxidation of Alcohols

Inspired by reactions catalyzed by galactose oxidase, a copper-containing enzyme, extensive studies were carried out on copper-based catalysts for alcohol oxidation using O2 as the terminal oxidant. Significant advances have been made towards the development of homogeneous and heterogeneous copper catalysts. These advances over the past decades are reviewed.