Chemistry

A Change of Face

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Science  23 Aug 2002:
Vol. 297, Issue 5585, pp. 1239
DOI: 10.1126/science.297.5585.1239c

In the Diels-Alder reaction, an alkene reacts with a diene to form a six-membered ring. A variety of stereochemical outcomes are possible with substituted reactants, and substituent groups can deactivate the reaction. Thus, the search for general catalysts of this reaction continues. Recently, Corey et al. reported a route in which proline-derived oxazaborolidines, in the presence of trifluoromethanesulfonic acid (TfOH), produce a strong Lewis acid that enables even α,β-unsaturated aldehydes to react efficiently and with stereochemical control. Often, such routes are not general, but Ryu et al. show that these catalysts can direct the reaction of even weaker dieneophiles, such as acrylic acid and ethyl vinyl ketone, with cyclopentadiene both in high yield and with high enantiomeric excess. The pretransition-state complex in these latter reactions (4) differs in face selectivity from that for the α,β-unsaturated aldehydes (3) in terms of the hydrogen bonds formed. — PDS

J. Am. Chem. Soc.124, 3808 (2002); J. Am. Chem. Soc. 10.1021/ja027468h.

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