Triflic acid (5mol%) is an efficient catalyst, which firstly applied to the anti-Markovnikov intermolecular
hydroamination of ethyl acrylate with 2-aminopyridines, sharply improves yields as high as 96%, reduces reaction times
as short as 12h. Moreover, the post-reaction process involves simple recrystallization in petroleum ether to obtain products
in purity as high as 99%. The reaction mechanism is verified by crossover experiments, based on the catalytic
mechanism of triflic acid previously proposed. The triflic acid is used for the reaction of a series of 2-aminopyridines with
ethyl acrylate, and all the derivatives of ethyl 3-[(pyridine-2-yl)amino]propionate are characterized by 1H/13C NMR and
HR-MS. The effect of electron-withdrawing/-donating substituent on the reaction is established by the reaction of
substituted aminopyridines with ethyl acrylate. The reactivity of 5-methyl-2-aminopyridine is higher than those of other
positional isomers of the same substituent. The reactivity of 2-aminopyridine with an electron-donating group is higher
than that with an electron-withdrawing group at the same position. 2-Aminopyridines with weak electron-withdrawing
substituent reacted more efficiently that those with strong electron-withdrawing substituents.
Keywords: Aminopyridines, anti-Markovnikov addition, catalytic mechanism, electron-withdrawing/-donating effect,
hydroamination, triflic acid.
Rights & PermissionsPrintExport