Although hydrazines cannot be directly added to non-activated, terminal acetylenes in the presence of mercury(II) salts, this difficulty was circumvented by treating hydrazines with 1-alkynylmercury trifluoroacetates (2); in this way, several hydrazones (4a–h) and 1-amino-1-aza-1,3-dienes (4i–m) were easily prepared.