Silylation and alkylation of thioamide dianions of N-arylmethyl secondary thioamides, and reduction of the resulting thioamides leading to secondary and primary amines

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N-arylmethyl aromatic thioamides were reacted with n-BuLi (2 equivalents), and then treated with silylpropyl chloride and silyl chlorides. As a result, these electrophiles were introduced to the carbon atom adjacent to the nitrogen atom of thioamides via thioamide dianions. The efficiency of the reaction was largely influenced by the substituents on the aromatic ring of thioamides. The reaction of thioamides having pyridyl groups was not always successful and depended on the position of the nitrogen atom of these groups. Reduction of the resulting thioamides with LiAlH4 proceeded smoothly to give the corresponding secondary N-1-silylarylmethyl amines in good yields. In contrast, the reduction of thioamides bearing pyridyl groups gave complex mixtures. In these cases, the use of DIBAH successfully gave the desired secondary amines.