Thiocyanic acid HSCN is added to some acetylenic compounds R1-C& 2 through a two- step one-pot procedure wich involves, first, the generation in CH2Cl2 of β-thiocyanato and/or β-isothiocyanato alkenyl mercuric coupounds R1-C (SCN)= CR2-Hg-by addition of mercury (II) thiocyanate Hg (SCN) 2 to R1-C& 2 then the substitution of mercury by hydrogen through acidic treatment. In proper conditions of stoechiometry and reaction ...