181026-82-4Relevant articles and documents
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.
Enantioselective Protonation of Ketene Bis(trimethylsilyl) Acetals Derived from α-Aryl-α-haloacetic Acids Using LBA
Ishihara, Kazuaki,Nakamura, Shingo,Yamamoto, Hisashi
, p. 513 - 517 (2007/10/03)
Optically active α-halocarboxylic acids and derivatives are important and versatile building blocks in organic synthesis. Lewis acid assisted chiral Bronsted acid (LBA) was recently prepared in situ from tin(IV) tetrachloride and optically pure binaphthol
