Transition metal-free amination of aryl halides-A simple and reliable method for the efficient and high-yielding synthesis of N-arylated amines

Article abstract of DOI:10.1016/j.tet.2008.11.072

A simple and reliable reaction protocol for the clean, fast, and high-yielding synthesis of various N-arylated amines derived from reactions of aryl halides with various (also sterically hindered) amines under transition metal-free reaction conditions is presented. Dioxane and KN(Si(CH₃)₃)₂ were found to be the ideal solvent and base for this transformation. The conversion rates and yields observed are excellent and in the majority of the reactions performed significantly higher than that obtained in their catalyzed versions. Furthermore, the selective synthesis of 6-halopyridin-2-amines and asymmetric pyridine-2,6-diamines (derived from consecutive reactions of 2,6-dibromopyridine and 2,6-dichloropyridine, respectively, with different amines) is possible in almost quantitative yields (relative to 2,6-dihalopyridine) within very short reaction times. Purification of the 6-halopyridin-2-amine intermediates is not necessary, allowing the synthesis of pyridine-2,6-diamines in 'one-pot'. However, catalysts are in many cases not required to efficiently and selectively couple aryl halides with amines, making transition metal-free versions of the Buchwald-Hartwig reaction extremely attractive for the synthesis of N-arylated amines with substrates containing substituents on the aryl halide, which either promote regioselectivity and/or do not require regioselective aminations.