Lithiation of N,N,N′,N′-tetraisopropylpyridine-2,6-dicarboxamide: synthesis, characterization and single crystal X-ray studies of chalcogen (Se/Te) derivatives of N,N,N′,N′-tetraisopropylpyridine-2,6-dicarboxamide.

Abstract: The lithiation of N,N,N′,N′-tetraisopropylpyridine-2,6-dicarboxamide (1) and its application in the synthesis of chalcogen (Se/Te) derivatives was investigated. It was found that the selectivity of the reaction changed with the change in the amount of n-BuLi used. The lithiation of 1 with 6.1 equiv of n-BuLi followed by subsequent reactions with selenium/tellurium and iodomethane exclusively afforded the monosubstituted chalcogen derivative (2a/2b) in excellent yield. However, the use of 2.1 or 4.2 equiv of n-BuLi gave two additional products along with 2a/2b. One of the isolated products corresponded to the double lithiation of 1 and the other to the ortho lithiation followed by nucleophilic addition of n-BuLi to the one of the two carbonyl moieties. The prepared compounds have been characterized by single crystal X-ray crystallography, NMR (1H, 13C, 77Se and 125Te), IR, UV–Visible and Mass spectroscopy. Crystal structure of N,N,N′,N′-tetraisopropyl-3,5-bis(methyltelluryl)pyridine-2,6-dicarboxamide (3b) reveals a strong intramolecular C O⋯Te secondary and intermolecular Te⋯π pyridyl interactions. [Copyright &y& Elsevier]