211870-31-4Relevant academic research and scientific papers
Enantioselective Protonation of Silyl Enol Ethers Catalyzed by a Chiral Pentacarboxycyclopentadiene-Based Bronsted Acid
An, Shaoyu,Li, Jun,Li, Pingfan,Yuan, Chao
supporting information, p. 1317 - 1320 (2019/06/19)
The enantioselective protonation of silyl enol ethers was realized in the presence of a pentacarboxycyclopenta-1,3-diene-based chiral Bronsted acid catalyst with water as an achiral proton source to give the corresponding α-aryl ketones in good yields and up to 75percent ee.
Chiral sulfinamide/achiral sulfonic acid cocatalyzed enantioselective protonation of enol silanes
Beck, Elizabeth M.,Hyde, Alan M.,Jacobsen, Eric N.
, p. 4260 - 4263 (2011/10/08)
The application of chiral sulfinamides and achiral sulfonic acids as a cocatalyst system for enantioselective protonation reactions is described. Structurally simple, easily accessible sulfinamides were found to induce moderate-to-high ee's in the formation of 2-aryl-substituted cycloalkanones from the corresponding trimethylsilyl enol ethers.
Chiral bronsted acid from a cationic gold(I) complex: Catalytic enantioselective protonation of silyl enol ethers of ketones
Cheon, Cheol Hong,Kanno, Osamu,Toste, F. Dean
, p. 13248 - 13251 (2011/10/10)
A chiral Bronsted acid has been developed from a cationic gold(I) disphosphine complex in the presence of alcoholic solvent and applied to the enantioselective protonation reaction of silyl enol ethers of ketones. Various optically active cyclic ketones were obtained in excellent yields and high enantioselectivities, including cyclic ketones bearing aliphatic substrates at the α-position. Furthermore, the application of this Bronsted acid was extended to the first Bronsted acid-catalyzed enantioselective protonation reaction of silyl enol ethers of acyclic substrates, regardless of their E/Z ratio.
Development of a new Lewis base-tolerant chiral LBA and its application to catalytic asymmetric protonation reaction
Cheon, Cheol Hong,Imahori, Tatsushi,Yamamoto, Hisashi
supporting information; experimental part, p. 6980 - 6982 (2010/11/02)
A new Lewis base-tolerant LBA (Lewis Acid Assisted Bronsted Acid) derived from La(OTf)3 and (S)-HOP has been developed as a new chiral Bronsted acid. This acid has been successfully applied as a catalyst to asymmetric protonation reactions of silyl enol ethers of 2-substituted cyclic ketones.
A bronsted acid catalyst for the enantioselective protonation reaction
Cheol, Hong Cheon,Yamamoto, Hisashi
supporting information; body text, p. 9246 - 9247 (2009/02/02)
A highly reactive and robust chiral Bronsted acid catalyst, chiral N-triflyl thiophosphoramide, was developed. The first metal-free Bronsted acid catalyzed enantioselective protonation reaction of silyl enol ethers was demonstrated using this chiral Bronsted acid catalyst. The catalyst loading could be reduced to 0.05 mol % without any deleterious effect on the enantioselectivity. Copyright
Enantioselective protonation of silyl enol ethers and ketene disilyl acetals with Lewis acid-assisted chiral Bronsted acids: Reaction scope and mechanistic insights
Nakamura, Shingo,Kaneeda, Masanobu,Ishihara, Kazuaki,Yamamoto, Hisashi
, p. 8120 - 8130 (2007/10/03)
Enantioselective protonation is a potent and efficient way to construct chiral carbons. Here we report details of the reaction using Lewis acid-assisted chiral Bronsted acids (chiral LBAs). The 1:1 coordinate complex of tin tetrachloride and optically active binaphthol ((R)- or (S)-BINOL) can directly protonate various silyl enol ethers and ketene disilyl acetals to give the corresponding α-aryl ketones and α-arylcarboxylic acids, respectively, with high enantiomeric excesses (up to 98% ee). A catalytic version of enantioselective protonation has also been achieved using stoichiometric amounts of 2,6-dimethylphenol and catalytic amounts of monomethyl ether of optically active BINOL in the presence of tin tetrachloride. This protonation is also effective for producing α-halocarbonyl compounds (up to 91% ee). DFT calculations on the B3LYP/LANL2DZ level show that the conformational structure of the chiral LBA and the orientation of activated proton on (R)-BINOLs are important for understanding the absolute stereochemistry of the products.
