PC Squared

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Science  11 Dec 2009:
Vol. 326, Issue 5959, pp. 1460-1461
DOI: 10.1126/science.326.5959.1460-d

Both urea and thiourea groups, which comprise two nitrogen centers respectively flanking a C=O or C=S center, have recently proven useful in asymmetric catalysis of a wide range of organic reactions. Zhu et al. have modified this scaffold by replacing the central carbonyl with a longer, two-carbon bridge contained within a cyclobutene-dione moiety, and then applied the new framework to the asymmetric addition of phosphites to nitroalkenes. The strained central square geometry of this catalyst proved highly effective for promoting the P-C bond-forming reaction, affording high yields and enantiomeric excesses with both aryl- and alkyl-substituted nitroalkenes. Reduction of the nitro group in these products would afford β-amino phosphonic acids, intriguing analogs of the more common amino (carboxylic) acids.

Angew. Chem. Int. Ed. 10.1002/anie.200904779 (2009).

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