Asymmetric Bromolactonization of 1,2-Disubstituted Olefinic Acids

Significance

Yeung and co-workers report a system for the asymmetric bromolactonization of 1,2-disubstituted olefinic acids. The products obtained are the anti-configured δ-lactones resulting from 6-endo cyclization. The authors employed the aminothiocarbamate catalyst 1, which is similar to their previously reported catalyst for the 5-exo cyclization of 1,1-disubstituted olefinic acids (J. Am. Chem. Soc. 2010, 132, 15474; highlighted in Synfacts 2011, 92). The reaction is supposed to proceed by a dual activation of NBS, wherein the Lewis-basic sulfur coordinates to the bromine and the succinimide carbonyl is activated by coordination to the thiocarbamate N-H bond. This model is also suited to rationalize the observed enantioselectivities by taking into account steric interactions between the substituents on the substrate and the catalyst.