The First Enantioselective Halo Aldol Reaction of Ethyl Propiolate and Aldehydes

The first enantioselective halo aldol reaction of ethyl propiolate with aldehydes has been established by using Jacobsen’s chiral cyclohexylsalen ligand. The reaction was conducted at −20 °C in dichloromethane with Et 2 AlI as the source of halogen and Lewis acid promoter. Excellent geometric selectivity (only the Z isomer) has been achieved for all 14 examples examined. The reaction works well with aromatic aldehydes; it also works with aliphatic aldehydes and α,β‐unsaturated aldehydes, albeit with diminished yields and ee . This method provides the first enantioselective synthesis of β‐iodo Morita−Baylis−Hillman (MBH) esters. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)