Base-catalyzed anti-Markovnikov hydroamination of vinylarenes - Scope, limitations and computational studies

The hydroamination of vinylarenes with primary and secondary amines was studied with catalytic amounts as low as 2 mol-% of LiN(SiMe3) 2/TMEDA. Reactions proceeded readily at 120°C in the absence of solvent to give selective anti-Markovnikov addition. Slow addition was observed at 25°C with either electron-deficient p-chlorostyrene or secondary cyclic amines such as pyrrolidine, piperidine, or morpholine. Primary amines were prone to a second hydroamination reaction to form tertiary amine byproducts. The selectivity for the mono(hydroamination) products could be improved with a two-fold excess of the amine. KN(SiMe3)2 showed higher catalytic activity but lower selectivity in comparison to that of LiN(SiMe 3)2, resulting in undesired C-H-activation by-products. The mechanism of the lithium-catalyzed hydroamination and the influence of TMEDA was studied with density functional theory. © Wiley-VCH Verlag GmbH & Co. KGaA, 2007.