Nature Chemistry 5, 510–517 (2013); published online 19 May 2013; corrected after print 22 May 2013.

In the print version of this paper, the stereochemical configuration of the β-lactone starting material 7 is drawn incorrectly ((R)-(–)-3-hydroxy-4,4,4-trichlorobutyric β-lactone purchased from Aldrich was used in this work). As a result, the stereochemical configurations of compounds 8 and 9 and the structure of the R group in Table 1 are also drawn incorrectly. These errors have now been corrected in the HTML and PDF versions of this Article.