Stereoselective Synthesis of (2Z)‑2,4-Dienamides via NBS-Mediated Allyloxyl Addition–Claisen Rearrangement–Dehydrobromination Cascade Reaction of Ynsulfonamides

An NBS-promoted allyloxyl addition–Claisen rearrangement–dehydrobromination cascade reaction has been developed. More than 20 substituted alkynylsulfonamides were reacted with allyl alcohols to generate (2Z)-2,4-dienamides in moderate to high yields. A mechanistic model has been proposed to account for the overall reaction sequence including the stereochemical outcome. Theoretical calculations suggested that a [3,3] sigmatropic rearrangement be the rate-limiting step.