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Bae, Han Yong
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Unprecedented Hydrophobic Amplification in Noncovalent Organocatalysis "on Water": Hydrophobic Chiral Squaramide Catalyzed Michael Addition of Malonates to Nitroalkenes

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Title
Unprecedented Hydrophobic Amplification in Noncovalent Organocatalysis "on Water": Hydrophobic Chiral Squaramide Catalyzed Michael Addition of Malonates to Nitroalkenes
Author
Bae, Han YongSong, Choong Eui
Keywords
noncovalent organocatalysis “on water”;  malonates as Michael donors;  hydrophobic hydration;  hydrophobic substituent effect;  Log P
Issue Date
201506
Publisher
AMER CHEMICAL SOC
Citation
ACS CATALYSIS, v.5, no.6, pp.3613 - 3619
Abstract
In this study, water was demonstrated to be an exceptionally efficient reaction medium for the noncovalent, hydrogen-bonding-promoted enantioselective Michael addition of malonates to diverse nitroolefins using cinchona-based squaramide catalysts. A significant increase in the reaction rate was observed when the reaction was performed "on water" rather than in the conventional organic solvents, because of the hydrophobic hydration effect. This hydrophobic amplification was significantly dependent upon the hydrophobicity of the C3-substituent (vinyl or ethyl) of cinchona-based catalysts. Thus, the use of more hydrophobic catalyst with an ethyl group at the C3-position, even a highly challenging Michael donor such as dimethyl methylmalonate was also smoothly converted to the desired adduct. Furthermore, because of the remarkable rate acceleration under "on water" conditions, the catalyst loading also significantly decreased. Thus, in the case of beta-ketoesters, even 0.01 mol % of catalyst loading was enough to complete the reaction at room temperature, affording the corresponding Michael adducts with perfect diastereo- and enantioselectivity (up to >99:1 d.r., up to 99% ee). The developed "on water" protocol was successfully applied for the scalable syntheses of an antidepressant (S)-rolipram and an anticonvulsant (S)-pregabalin
URI
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DOI
http://dx.doi.org/10.1021/acscatal.5b00685
ISSN
2155-5435
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