945656-70-2Relevant academic research and scientific papers
Modified chiral triazolium salts for enantioselective benzoin cyclization of enolizable keto-aldehydes: Synthesis of (+)-sappanone B
Takikawa, Hiroshi,Suzuki, Keisuke
, p. 2713 - 2716 (2007)
Equation Presented Asymmetric synthesis of (+)-sappanone B (1), a natural product with a 3-hydroxy chromanone structure, was achieved via enantioselective benzoin cyclization by using a modified Rovis catalyst and triethylamine. This catalyst enabled the
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.
Rh-catalyzed carbonyl hydroacylation: an enantioselective approach to lactones
Shen, Zengming,Khan, Hasan A.,Dong, Vy M.
, p. 2916 - 2917 (2008/10/09)
This communication describes the design and execution of a novel approach to forming chiral lactones via C-H bond activation. The strategy features an unprecedented enantioselective Rh-catalyzed hydroacylation of carbon-oxygen double bonds. Representative keto-aldehydes (derived from salicylaldehyde) undergo cyclization with complete regioselectivity to afford seven-membered lactones in great enantiomeric excess (≥99% ee). The basicity of the phosphine ligand is shown to play a critical role in promoting hydroacylation over competitive decarbonylation. Copyright
