An Approach to Enantioselective 5‐endo Halo‐Lactonization Reactions

Enantioselective lactonization of 4‐substituted but‐3‐enoic acids using iodobis(N‐methylephedrine) hexafluoroantimonate in dichloromethane at low temperatures is reported. The presence of bis(N‐methylephedrine)silver(I) hexafluoroantimonate, derived from the excess amounts of N‐methylephedrine and silver hexafluoroantimonate that were necessary for the generation of the iodo complex in the reaction mixture, is crucial for the success of this reaction. The different parameters of these cyclization reactions have been examined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)