Ruthenium complex-controlled catalytic N-mono- or N,N-dialkylation of heteroaromatic amines with alcohols

Article abstract of DOI:10.1021/jo9516289

Heteroaromatic amines were N-alkylated with primary alcohols at 150-200°C in the presence of a catalytic amount of various ruthenium complexes to give the corresponding monoalkylated and dialkylated amines in good to high yields. For example, 2-aminopyridine reacted with an excess of ethanol at 180°C for 20 h in the presence of dichlorotris(triphenylphosphine)ruthenium [RuCl₂-(PPh₃)₃] to give 2-(ethylamino)pyridine (1) and 2-(diethylamino)pyridine (2) in 9% and 70% yields, respectively. On the other hand, when (η⁴-1,5-cyclooctadiene)(η ⁶-1,3,5-cyclooctatriene)ruthenium [Ru(cod)(cot)] was used as a catalyst, even in the presence of excess ethanol, 1 was obtained in 85% yield with high selectivity. The addition of tertiary phosphines and phosphites to Ru(cod)-(cot) increased the yield of the dialkylated amine.