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Synthesis

Organocatalyst Passes Chirality Along

Supramolecular catalyst could point the way to a powerful new strategy for finding novel organocatalysts

by Amanda T. Yarnell
August 31, 2009 | APPEARED IN VOLUME 87, ISSUE 35

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Credit: Courtesy of Takashi Ooi
A chiral phosophonium cation and three achiral small organic molecules self-assemble into a chiral catalyst through hydrogen bonding (P = purple, N = blue, O = red, C = gray, H = white).
1a(OPh)3H2cxd_opt.jpg
Credit: Courtesy of Takashi Ooi
A chiral phosophonium cation and three achiral small organic molecules self-assemble into a chiral catalyst through hydrogen bonding (P = purple, N = blue, O = red, C = gray, H = white).

An asymmetric catalyst that assembles spontaneously from simple organic components could point the way to a powerful new strategy for finding novel organocatalysts, according to researchers in Japan. Takashi Ooi, Daisuke Uraguchi, and Yusuke Ueki of Nagoya University built the catalyst simply by mixing a chiral tetraaminophosphonium cation, two phenols, and a phenoxide anion in solution (Science, DOI: 10.1126/science.1176758). The catalyst is held together by relatively weak hydrogen-bonding and ionic interactions. It’s remarkable that stereochemical information in the chiral phosphonium cation is effectively relayed by achiral phenols all the way to the remotely located phenoxide anion, comments Sukwon Hong of the University of Florida, Gainesville. The extended chiral environment that results allows the catalyst to promote the highly stereoselective conjugate addition of acyl anion equivalents, Ooi’s team finds. The catalyst’s discovery “points the way to a combinatorial strategy for finding new supramolecular organocatalysts,” says Joost N. H. Reek of the University of Amsterdam. Such a strategy is already being explored to make supramolecular transition-metal catalysts, he notes.

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