882883-57-0Relevant academic research and scientific papers
Rare-Earth-Metal-Catalyzed Kinetic Resolution of Chiral Aminoalkenes via Hydroamination: The Effect of the Silyl Substituent of the Binaphtholate Ligand on Resolution Efficiency
Nguyen, Hiep N.,Hultzsch, Kai C.
, p. 2592 - 2601 (2019/03/21)
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 kfast/kslow 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.
C1-symmetric rare-earth-metal aminodiolate complexes for intra- and intermolecular asymmetric hydroamination of alkenes
Reznichenko, Alexander L.,Hultzsch, Kai C.
, p. 1394 - 1408 (2013/05/21)
A series of novel C1-symmetric aminodiolate rare-earth-metal complexes have been prepared via arene elimination from [Ln(o-C 6H4CH2NMe2)3] (Ln = Y, Lu) and the corresponding aminodiol proligand. The NOBIN-derived aminodiolate ligands feature sterically demanding triphenylsilyl and methyldiphenylsilyl ortho substituents on the naphtholate moiety and substituents of varying steric demand ranging from tert-butyl to tris(3,5-xylyl)silyl on the phenolate moiety. Complexes with a triphenylsilyl substituent on the naphtholate moiety displayed good catalytic activity in the hydroamination/cyclization of aminoalkenes, while complexes with a methyldiphenylsilyl substituent exhibited somewhat lower reactivity. The highest enantioselectivities for five- and six-membered-ring formation were observed utilizing complex 9c-Lu (R1 = Ph, R 2 = Me, R3 = SiPh3) in the cyclization of (2,2-diphenylpent-4-enyl)amine (92% ee, Nt = 200 h-1 at 25 C) and (2,2-diphenylhex-5-enyl)amine (73% ee, Nt = 20 h-1 at 25 C). The complexes can be applied in asymmetric intermolecular hydroaminations of 1-heptene and 4-phenyl-1-butene with benzylamine with enantioselectivities of up to 40% ee using complex 9b-Y (R1 = Ph, R2 = Me, R3 = SiPh2Me). Here the higher catalytic activities are achieved with catalysts having a methyldiphenylsilyl substituent on the naphtholate moiety. Lanthanum aminodiolate catalysts generated in situ from [La{CH(C6H5)NMe2} 3] did not exhibit improved catalytic activity in the intermolecular hydroamination in comparison to the corresponding yttrium and lutetium catalysts. The overall catalytic activities of the aminodiolate complexes are somewhat diminished in comparison to previously studied binaphtholate complexes due to the presence of the additional amine donor site in the ligand framework.
Kinetic resolution of aminoalkenes by asymmetric hydroamination: A mechanistic study
Reznichenko, Alexander L.,Hampel, Frank,Hultzsch, Kai C.
scheme or table, p. 12819 - 12827 (2010/06/17)
The kinetic resolution of chiral aminoalkenes by hydroamination-cyclization was studied by using 3,3'-bis(triarylsilyl)-substituted binaphtholate rare-earth-metal complexes. The resolution of 1-arylaminopentenes proceeds with high efficiency and high irans-diastereoselectivity, whereas the resolution process of 1-alkylaminopentenes suffers from decreasing resolution efficiency with increasing steric demand of the aliphatic substituent. Kinetic studies of the matching and mismatching substrate-catalyst pair by using enantiopure substrates and either the (R)- or (S)-binaphtholate catalysts revealed that the difference in resolution efficiency stems from a shift of the Curtin-Hammett pre-equilibrium. Al-though 1-arylaminopentenes favor the matching substrate-catalyst complex, preference for the mismatching substrate-catalyst complex for 1-alkylaminopentenes diminishes resolution efficiency. Nevertheless, the relative cyclization rate for the two diastereomeric substrate-catalyst complexes remains in a typical range of 7-10:1. Plausible attractive π interactions between the aryl substituent and either the metal center or the aromatic system of the bis(triarylsilyl)-substituted binaphtholate ligand may explain increased sta-bility of the matching substrate-catalyst complex. Incidentally, the methoxymethyl (MOM)-substituted aminopentene 3g also exhibited a strong preference for the matching substrate-catalyst complex, possibly due to the chelating nature of the MOM substituent. The proximity of the stereocenter to the amino group in the aminoalkene substrate was crucial to achieve good kinetic resolution efficiency. The more remote β-phenyl substituent in 2-phenylpent-4-en-l-amine (5) resulted in diminished discrimination of the substrate enantiomers with respect to the relative rate of cyclization of the two substrate-catalyst complexes and a Curtin-Hammett preequilibrium close to unity.
3,3′-Bis(trisarylsilyl)-substituted binaphtholate rare earth metal catalysts for asymmetric hydroamination
Gribkov, Denis V.,Hultzsch, Kai C.,Hampel, Frank
, p. 3748 - 3759 (2007/10/03)
Chiral 3,3′-bis(trisarylsilyl)-substituted binaphtholate rare earth metal complexes (R)-[Ln{Binol-SiAr3}(o-C6H 4CH2NMe2)(Me2NCH2Ph)] (Ln = Sc, Lu, Y; Binol-SiAr3 = 3,3′-bis(trisarylsilyl)-2,2′- dihydroxy-1,1′-binaphthyl; Ar = Ph (2-Ln), 3,5-xylyl (3-Ln)) and (R)-[La{Binol-Si(3,5-xylyl)3}{E(SiMe3)2}(THF) 2] (E = CH (4a), N (4b)) are accessible via facile arene, alkane, and amine elimination. They are efficient catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, giving TOF of up to 840 h -1 at 25 °C for 2,2-diphenyl-pent-4-enylamine (5c) using (R)-2-Y. Enantioselectivities of up to 95% ee were achieved in the cyclization of 5c with (R)-2-Sc. The reactions show apparently zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, but rates depend on total amine concentrations. Activation parameters for the cyclization of pent-4-enylamine using (R)-2-Y (ΔH(S)? = 57.4-(0.8) kJ mol-1 and ΔS(S)? = -102(3) J K-1 mol-1; ΔH(R)? = 61.5(0.7) kJ mol-1 and ΔS(R)? = -103(3) J K-1 mol -1) indicate a highly organized transition state. The binaphtholate catalysts were also applied to the kinetic resolution of chiral α-substituted aminoalkenes with resolution factors f of up to 19. The 2,5-disubstituted aminopentenes were formed in 7:1 to ≥50:1 trans diastereoselectivity, depending on the size of the α-substituent of the aminoalkene. Rate studies with (S)-1-phenyl-pent-4-enylamine ((S)-15e) gave the activation parameters for the matching (ΔH? = 52.2(2.8) kJ mol -1, ΔS? = -127(8) J K-1 mol-1 using (S)-2-Y) and mismatching (ΔH? = 57.7(1.3) kJ mol -1, ΔS? = -126(4) J K-1 mol-1 using (R)-2-Y) substrate/catalyst combination. The absolute configuration of the Mosher amide of (2S)-2-methyl-4,4-diphenyl-pyrrolidine and (2R)-methyl-(5S)- phenyl-pyrrolidinium chloride, prepared from (S)-15e, were determined by crystallographic analysis. Catalyst (R)-4a showed activity in the anti-Markovnikov addition of n-propylamine to styrene.
Chiral oxime ethers in asymmetric synthesis. Part 4. Asymmetric synthesis of N-protected amines and β-amino acids by the addition of organometallic reagents to ROPHy/SOPHy-derived aldoximes
Hunt, James C. A.,Lloyd, Cephas,Moody, Christopher J.,Slawin, Alexandra M. Z.,Takle, Andrew K.
, p. 3443 - 3454 (2007/10/03)
Addition of organolithium or Grignard reagents to (R)- or (S)-O-(1-phenylbutyl)aldehyde oximes 1 in the presence of boron trifluoride-diethyl ether results in the formation of hydroxylamines 2 in good to excellent diastereoselectivity. Subsequent cleavage of the N-O bond with zinc-acetic acid-ultrasound, and carbamate formation, gives N-protected amines 3 in good enantiomeric purity (77-100% ee). When allylmagnesium bromide was used as the organometallic reagent, the resulting hydroxylamines were converted into β-amino acid derivatives 4 and γ-aminb alcohols 5. The Royal Society of Chemistry 1999.
