The development of efficient methods for the synthesis of nitrogen-containing compounds remains an important goal in contemporary catalysis research because of the central role of this class of compounds in biological systems and pharmaceutical applications.[1] The addition of an amine N À H bond to a carbon-carbon multiple bond, so-called hydroamination, [2] is a reaction with great synthetic potential, as it not only reduces the formation of waste owing to its atom economy, but it utilizes also very simple starting materials. The development of novel catalyst systems for hydroamination has seen significant progress in the last two decades, [2,3] but the intermolecular hydroamination of unactivated alkenes with simple amines remains very challenging. [4] Therefore, it is not too surprising that asymmetric hydroamination reactions [5] have been studied predominantly in intramolecular reactions. [6, 7] Intermolecular reactions have been reported only sporadically and all of these studies were limited to the reaction between aniline derivatives and activated alkenes, such as vinyl arenes, [8] 1,3-dienes, [9] and strained bicyclic alkenes.[10] The first enantioselective goldcatalyzed addition of cyclic ureas to unactivated alkenes in up to 78 % ee was reported recently by Widenhoefer and coworkers.[11] Herein we report the stereoselective addition of simple amines to unactivated alkenes utilizing chiral rareearth-metal-based catalysts.Catalyst systems based on rare-earth-metal complexes exhibit high catalytic activity, in particular in intramolecular hydroaminations, [2, 3f] whereas intermolecular hydroaminations are significantly more difficult to achieve as a result of the unfavorable competition between weakly coordinating alkenes and strongly coordinating amines. [4a,b, 6b, 12] We have previously reported on efficient biphenolate and binaphtholate rare-earth-metal catalysts, [6b, 13] which can catalyze the intramolecular hydroamination of aminoalkenes with high activity and up to 95 % ee. Preliminary studies with a corresponding binaphtholate lanthanum complex for the reactions of styrene [6b] and 1,3-cyclohexadiene [14] indicated the potential applicability of these systems in asymmetric intermolecular hydroaminations. As the lanthanum catalyst showed rather low selectivity [14] we decided to utilize the generally more selective yttrium and lutetium catalysts in our study. For the initial catalyst screening we chose the reaction of 1-heptene with benzylamine.

Eine harte Nuss zu knacken: Die asymmetrische intermolekulare Markownikow‐Addition einfacher Amine an nichtaktivierte Alkene gelingt mithilfe von Binaphtholat‐Seltenerdmetallkatalysatoren mit bis zu 61 % ee und 73 % de, wenn R2 ein stereogenes Zentrum enthält.

The series of novel 3,3′-bis(trisarylsilyl)-and 3,3′-bis(arylalkylsilyl)-substituted binaphtholate rare-earthmetal complexes 2a−i (SiR 3 = Si(o-biphenylene)Ph (a), SiCyPh 2 (b), Si-t-BuPh 2 (c), Si(i-Pr) 3 (d), SiCy 2 Ph (e), Si(2-tolyl)Ph 2 (f), Si(4-t-Bu-C 6 H 4 ) 3 (g), Si(4-MeO-C 6 H 4 )Ph 2 (h), SiBnPh 2 (i)) have been prepared via arene elimination from [Ln(o-C 6 H 4 CH 2 NMe 2 ) 3 ] (Ln = Y, Lu) and the corresponding 3,3′-bis(silyl)-substituted binaphthol. The complexes exhibit high catalytic activity in the hydroamination/ cyclization of aminoalkenes, with activities exceeding 1000 h −1 for (R)-2f-Ln, (R)-2g-Ln, and (R)-2h-Ln in the cyclization of 2,2-diphenylpent-4-enylamine (3a) at 25 °C, while the rigid dibenzosilole-substituted complexes (R)-2a-Ln and the triisopropylsilyl-substituted complexes (R)-2d-Ln exhibited the lowest activity in the range of 150−270 h −1 . Catalysts (R)-2b-Lu, (R)-2c-Lu, (R)-2f-Lu, and (R)-2i-Lu provide the highest selectivities for the majority of the substrates, while the yttrium congeners are usually less selective. The highest enantioselectivities of 96% ee were observed using (R)-2a-Lu and (R)-2c-Lu in the cyclization of (4E)-2,2,5-triphenylpent-4-enylamine (9). The reactions show apparently zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, with some reactions exhibiting a slightly accelerated rate at high conversion due to a shift in the equilibrium between a less active, higher coordinate catalyst species in favor of a more active, lower coordinate species as a result of weaker binding of the hydroamination product in comparison to the aminoalkene substrate. The shift in equilibrium from the higher to the lower coordinate species is also entropically favored at elevated temperatures, which results in an unusual increase in selectivity in the cyclization of 2,2-dimethylpent-4-enylamine (3d), presumably due to a higher selectivity of the lower coordinate catalyst species. All binaphtholate yttrium complexes, except (R)-2a-Y, are catalytically active in the intermolecular hydroamination of benzylamines with terminal alkenes. The highest selectivity of 66% ee was observed for the reaction of benzylamine with 4-phenyl-1-butene using (R)-2h-Y at 110 °C.

The kinetic resolution of α‐substituted aminopentenes via intramolecular hydroamination was investigated using various 3,3′‐silyl‐substituted binaphtholate yttrium catalysts. High efficiencies in the kinetic resolution were observed for methyl‐, benzyl‐, and phenyl‐substituted substrates utilizing the cyclohexyldiphenylsilyl‐substituted catalyst 2c with resolution factors reaching as high as 90(5) for hex‐5‐en‐2‐amine ( 3a ). Kinetic analysis of the enantioenriched substrates with the matching and mismatching catalyst revealed that the efficiency of catalyst 2c benefits significantly from a favorable Curtin–Hammett pre‐equilibrium and by a large k fast /k slow ratio. Other binaphtholate catalysts were less efficient due to a less favorable Curtin–Hammett pre‐equilibrium, which often favored the mismatching substrate‐catalyst combination. Cyclization of the matched substrate proceeds generally with large trans ‐selectivity, whereas the trans/cis ‐ratio for mismatched substrates is significantly diminished, favoring the cis ‐cyclization product isomer in some instances.

The reaction is studied in the presence of binaphtholate yttrium complexes.