The BF3•OEt2-Assisted Conversion of Nitriles into Thioamides with Lawesson's Reagent

A method for the thiolysis of nitriles by applying Lawesson's reagent and facilitated by the addition of boron trifluoride-diethyl ether complex is reported. The method opens an easy access to primary thioamides. Aromatic, benzylic, and aliphatic nitriles were converted into the corresponding thioamides in high to quantitative yields (even in unfavorable cases, e.g., ortho-substituted benzonitriles). The reaction was performed in 1,2-dimethoxy-ethane-tetrahydrofuran or toluene-diethyl ether solvent mixtures at 20-50 degrees C, and exhibited considerable selectivity in the case of multifunctional nitrile substrates, such as cyanomethyl N-acetylphenylalaninate, benzoylacetonitrile, 4-cyanobenzamide, 4-acetylbenzonitrile, or pent-3-enenitrile.