AlCl3-NaI(NaBr)-t-BuOH: mild, chemo- and stereoselective reagents for hydrohalogenation of propiolic derivatives

(Z)-β-Iodo-propenamides and -β-iodo-propenoic esters were selectively prepared in high yields, at room temperature, through reaction of 2-propynamides and 2-propynoic esters, respectively, with AlCl₃ and NaI in the presence of t-BuOH in dichloromethane. These experimental conditions are compatible with the presence of acid sensitive acetal groups. Alternative use of EtOH or H₂O in place of t-BuOH was investigated. (Z)-Bromo-propenamides and corresponding esters were prepared according to a similar procedure using sodium bromide in refluxing acetonitrile.