Ruthenium Complex-Controlled CatalyticN-Mono- orN,N-Dialkylation of Heteroaromatic Amines with Alcohols

Abstract

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)(η⁶-1,3,5-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.