188549-18-0Relevant academic research and scientific papers
Cobalt-Catalyzed Reductive C-O Bond Cleavage of Lignin β-O-4 Ketone Models via in Situ Generation of the Cobalt-Boryl Species
Gao, Kecheng,Xu, Man,Cai, Cheng,Ding, Yanghao,Chen, Jianhui,Liu, Bosheng,Xia, Yuanzhi
supporting information, p. 6055 - 6060 (2020/08/12)
An efficient and mild method for reductive C-O bond cleavage of lignin β-O-4 ketone models was developed to afford the corresponding ketones and phenols with PDI-CoCl2 as the precatalyst and diboron reagent as the reductant. The synthetic utility of the methodology was demonstrated by depolymerization of a polymeric model and gram-scale transformation. Mechanistic studies suggested that this transformation involves steps of carbonyl insertion, 1,2-Brook type rearrangement, β-oxygen elimination, and rate-limiting regeneration of the catalytic active Co-B species.
Highly efficient synthesis of functionalized α-oxyketones: Via Weinreb amides homologation with α-oxygenated organolithiums
Pace, Vittorio,Murgia, Irene,Westermayer, Sophie,Langer, Thierry,Holzer, Wolfgang
supporting information, p. 7584 - 7587 (2016/07/06)
An efficient, chemoselective homologation of Weinreb amides to the corresponding variously substituted α-oxyketones has been developed via the addition of lithiated α-oxygenated species. This one-step, experimentally easy, high yielding protocol is amenable not only for accessing simple α-oxyketones but also for more complex substituted ones ranging from primary and secondary alkyl-type to aromatic ones. Full delivery of the stereochemical information contained in the starting materials is observed through both the employment of enantioenriched Weinreb amides and optically active organolithium species.
Mechanistic insights into the rhodium-catalyzed intramolecular ketone hydroacylation
Shen, Zengming,Dornan, Peter K.,Khan, Hasan A.,Woo, Tom K.,Dong, Vy M.
supporting information; experimental part, p. 1077 - 1091 (2009/06/28)
[Rh((fl)-DTBM-SEGPHOS)]BF4 catalyzes the intramolecular hydroacylation of ketones to afford seven-membered lactones in large enantiomeric excess. Herein, we present a combined experimental and theoretical study to elucidate the mechanism and origin of selectivity in this C-H bond activation process. Evidence is presented for a mechanistic pathway involving three key steps: (1) rhodium(I) oxidative addition into the aldehyde C-H bond, (2) insertion of the ketone C=O double bond into the rhodium hydride, and (3) C-O bond-forming reductive elimination. Kinetic isotope effects and Hammett plot studies support that ketone insertion isthe turnover-limiting step. Detailed kinetic experiments were performed using both 1,3- bis(diphenylphosphino)propane (dppp) and (R)-DTBM-SEGPH OS as ligands. With dppp, the keto-aldehyde substrate assists in dissociating a dimeric precatalyst 8 and binds an active monomeric catalyst 9. With [Rh((R)-DTBM-SEGPHOS)]BF4, there is no induction period and both substrate and product inhibition are observed. In addition, competitive decarbonylation produces a catalytically inactive rhodium carbonyl species that accumulates over the course of the reaction. Both mechanisms were modeled with a kinetics simulation program, and the models were consistent with the experimental data. Density functional theory calculations were performed to understand more elusive details of this transformation. These simulations support that the ketone insertion step has the highest energy transition state and reveal an unexpected interactionbetween the carbonyl-oxygen lone pair and a Rh d-orbital in this transi tion state structure. Finally, a model based on the calculated transition-state geometry is proposed to rationalize the absolute sense of enantioinduction observed using (R)-DTBM-SEGPHOS as the chiral ligand.
Palladium (0) catalyzed nucleophilic substitution on 2-cyclopropylidene-phenoxy ethanes
Bernard, Angela M.,Piras, Pier P.
, p. 709 - 723 (2007/10/03)
2-cyclopropylidene-phenoxy ethanes 5, 2-substituted with alkyl, aryl or heterocyclic groups are readily obtained in high yields by the Wittig reaction of the easily accessible α-phenoxy etanones 4 with (3-bromo propyl) triphenylphosphonium bromide. They react with complete regioselectivity in palladium (0) catalyzed nucleophilic substitutions with a series of soft carbon nucleophiles giving an easy entry to 5,6-methanoamino acids.
