Lewis acid induced rearrangement of 2,3-epoxy sulfides; regiospecific trapping of thiiranium ion intermediates with nitrogen heterocycles and amides. Use of imines as nucleophilic equivalents for the selective monoalkylation of primary amines

Article abstract of DOI:10.1016/0040-4020(96)00036-1

The Lewis acid induced conversion of 2,3-epoxy sulfides into the corresponding 3-trimethylsilyloxy-1,2-thiiranium ions is described. Such intermediates react with silylated nitrogen heterocycles and amides regiospecifically to form 1-substituted-3-hydroxy-2-thioethers in good to moderate yields with full stereochemical control. Exclusive N-alkylation is observed. When simple primary amines are used as nucleophiles, only products of polyalkylation are isolated. However, imines can be effectively used as the nucleophilic equivalent of a primary amine, the initially formed iminium ions being readily hydrolysed by aqueous base to liberate a secondary amine, the product of overall selective monoalkylation of a primary amine.