Synthesis and Reactivity of a Stable Prototropic Isomer of 2-Acetyl-3-methylpyrrole

4-Isocyanobut-1-ene reacted rapidly with acetyl bromide to afford an unstable imidoyl bromide adduct. Subsequent in situ cyclization under Heck conditions generated a stable prototropic isomer of 2-acetyl-3-methylpyrrole. The reactivity of this molecule toward ­acids, bases, and oxidants was explored, and its conversion into an α-methylidene γ-lactam was demonstrated. In protonated form, the molecule functioned as a reactive dienophile in Diels–Alder reactions.