34733-55-6Relevant articles and documents
Electrochemical and Photocatalytic Oxidative Coupling of Ketones via Silyl Bis-enol Ethers
Caravana, Aidan C.,Nagasing, Benjamin,Dhanju, Sandeep,Reynolds, Rebekah G.,Weiss, Emily A.,Thomson, Regan J.
supporting information, p. 6600 - 6611 (2021/05/29)
Diastereoselective oxidative coupling of ketones through a silyl bis-enol ether intermediate by anodic and photocatalytic oxidation is reported. These methods provide several 1,4-diketones in good yields without the need for stoichiometric metal oxidants. The strategic use of a silicon tether enables the coupling of both aromatic and aliphatic ketones as well as the synthesis of quaternary centers. Cyclic voltammetry is used to gain insight into the oxidation events of the reaction.
Mechanistic Investigation of Enantioconvergent Kumada Reactions of Racemic α-Bromoketones Catalyzed by a Nickel/Bis(oxazoline) Complex
Yin, Haolin,Fu, Gregory C.
supporting information, p. 15433 - 15440 (2019/10/22)
In recent years, a wide array of methods for achieving nickel-catalyzed substitution reactions of alkyl electrophiles by organometallic nucleophiles, including enantioconvergent processes, have been described; however, experiment-focused mechanistic studies of such couplings have been comparatively scarce. The most detailed mechanistic investigations to date have examined catalysts that bear tridentate ligands and, with one exception, processes that are not enantioselective; studies of catalysts based on bidentate ligands could be anticipated to be more challenging, due to difficulty in isolating proposed intermediates as a result of instability arising from coordinative unsaturation. In this investigation, we explore the mechanism of enantioconvergent Kumada reactions of racemic α-bromoketones catalyzed by a nickel complex that bears a bidentate chiral bis(oxazoline) ligand. Utilizing an array of mechanistic tools (including isolation and reactivity studies of three of the four proposed nickel-containing intermediates, as well as interrogation via EPR spectroscopy, UV-vis spectroscopy, radical probes, and DFT calculations), we provide support for a pathway in which carbon-carbon bond formation proceeds via a radical-chain process wherein a nickel(I) complex serves as the chain-carrying radical and an organonickel(II) complex is the predominant resting state of the catalyst. Computations indicate that the coupling of this organonickel(II) complex with an organic radical is the stereochemistry-determining step of the reaction.
Bioinspired total synthesis of tetrahydrofuran lignans by tandem nucleophilic addition/redox isomerization/oxidative coupling and cycloetherification reactions as key steps
Jagtap, Pratap R.,Císa?ová, Ivana,Jahn, Ullrich
supporting information, p. 750 - 755 (2018/02/09)
A very short three-step approach to trans,trans,trans-2,5-diaryl-3,4-dimethyltetrahydrofuran lignans is reported. The carbon skeleton is assembled in a single step based on an unprecedented tandem reaction consisting of 1,2-addition of aryllithium reagents to α,β-unsaturated aldehydes, ruthenium-catalyzed redox isomerization of the resulting alkoxides to enolates and their dimerization triggered by single electron oxidation. The resulting 2,3-dialkyl-1,4-diketones form with moderate to good d/l-diastereoselectivity and are transformed to the target tetrahydrofuran lignans by reduction and diastereoselective cycloetherification.
