- Formation of boroxine: Its stability and thermodynamic parameters in solution
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Condensation of three boronic acids proceeding at room temperature gave their corresponding boroxines; NMR spectral measurements revealed that the reaction was reversible at room temperature, that electron-donating groups supported the formation of boroxine, and that entropically driven forces promoted the formation of boroxine in solution.
- Tokunaga, Yuji,Ueno, Hiroki,Shimomura, Youji,Seo, Toshihiro
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- Boroxine nanotubes: Moisture-sensitive morphological transformation and guest release
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Boroxines, (R-BO)3, which can be easily synthesized via a dehydration reaction of boronic acids, R-B(OH)2, selectively self-assemble in toluene into nanofibers, nanorods, nanotapes, and nanotubes, depending on the aromatic substituent (R). Spectroscopic measurements show that the nanotube consists of a J-aggregate of the boroxine. Humidification converts the morphology from the nanotube to a sheet as a result of the hydrolysis of the boroxine components and subsequent molecular-packing rearrangement from the J-aggregate to an H-aggregate. Such a transformation leads to the compulsive release of guest molecules encapsulated in the hollow cylinder of the nanotube. The hydrolysis and the molecular-packing rearrangement described above are suppressed by coordination of pyridine to the boron atom, with the resulting moiety acting as a Lewis acid of the boroxine component. The pyridine-coordinated nanotube is transformed into a helical coil by humidification. Guest release during the nanotube-to-helical-coil transformation is much slower than during the nanotube-to-sheet transformation, but faster than from a nanotube that did not undergo morphological transformation. The storage and release of guest molecules from the boroxine nanotubes can be precisely controlled by adjusting the moisture level and the concentration of Lewis bases, such as amines. Self-assembly of boroxines in toluene produce various nanostructures, including nanotubes, depending on the boroxines' aromatic substituents. Humidification-induced morphological transformations from nanotubes to sheets or helical coils are observed, accompanied by the hydrolysis of the boroxine components and a molecular-packing rearrangement from J- to H-aggregates. These morphological changes enable the precisely controlled release of guest molecules encapsulated in the nanotubes' hollow cylinders.
- Ishikawa, Kazuyuki,Kameta, Naohiro,Masuda, Mitsutoshi,Asakawa, Masumi,Shimizu, Toshimi
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- Nickel(II)-Catalyzed Addition of Aryl and Heteroaryl Boroxines to the Sulfinylamine Reagent TrNSO: The Catalytic Synthesis of Sulfinamides, Sulfonimidamides, and Primary Sulfonamides
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We report a redox-neutral Ni(II)-catalyzed addition of (hetero)aryl boroxines to N-sulfinyltritylamine (TrNSO). The reactions use a catalyst generated from the combination of commercial, air-stable NiCl2·(glyme) and a commercially available bipyridine lig
- Lo, Pui Kin Tony,Willis, Michael C.
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supporting information
p. 15576 - 15581
(2021/10/02)
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- Highly Enantioselective Ferrocenyl Palladacycle-Acetate Catalysed Arylation of Aldimines and Ketimines with Arylboroxines
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Benzylic N-substituted stereocenters constitute a frequent structural motif in drugs. Their highly enantioselective generation is hence of technical importance. An attractive strategy is the arylation of imines with organoboron reagents. Chiral Rh complexes have reached a high level of productivity for this reaction type. In this article we describe that an electron rich PdIIcatalyst also performs well in the arylation of aldimines, comparable to the best Rh catalysts. The ferrocenyl palladacycle-acetate catalyst allows for a broad substrate scope and very high enantioselectivities. Commonly observed side reactions like aryl–aryl homocouplings and imine hydrolysis could be blocked. Mechanistic studies implicate that a) the acetate ligand is crucial for transmetallation, b) the active catalyst is most likely a palladacycle-OAc monomer, c) the rate limiting step is probably the product release. By added KOAc the arylation could also be applied to ketimines.
- Schrapel, Carmen,Frey, Wolfgang,Garnier, Delphine,Peters, René
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supporting information
p. 2448 - 2460
(2017/02/23)
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- Palladium(II)-Catalyzed Enantioselective Synthesis of α-(Trifluoromethyl)arylmethylamines
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We describe a method for the synthesis of α-(trifluoromethyl)arylmethylamines that consists of the palladium(II)-catalyzed addition of arylboroxines to imines derived from trifluoroacetaldehyde. Palladium acetate is used as a catalyst with electron-neutral or electron-rich arylboroxines, and it was found that addition of an ammonium or silver salt was crucial to promote the reaction of electron-poor boroxines. With (S)-t-Bu-PyOX as the chiral ligand, this method delivers a variety of α-trifluoromethylated amines in 57-91% yield and with greater than 92% ee in most cases.
- Johnson, Thomas,Luo, Bo,Lautens, Mark
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p. 4923 - 4930
(2016/07/06)
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- Diastereoselective synthesis of vicinally bis(trifluoromethylated) alkylboron compounds through successive insertions of 2,2,2-trifluorodiazoethane
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The usefulness of embedded CF3 substituents within organic substructures necessitates the development of diverse methods for incorporating this functional group. A recently reported route to α-trifluoromethylated alkylboron compounds by an α-transfer mechanism has now been extended to the synthesis of unprecedented, vicinally ditrifluoromethylated alkylboron compounds in a diastereoselective fashion. The utility of these products is highlighted by conversion of the C-B bond into other functional groups.
- Molander, Gary A.,Ryu, Da Weon
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supporting information
p. 14181 - 14185
(2015/02/19)
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- Rhodium-catalyzed asymmetric hydroarylation of 3-pyrrolines giving 3-arylpyrrolidines: Protonation as a key step
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A hydroxorhodium complex coordinated with (R)-segphos was found to catalyze the hydroarylation of 3-pyrrolines with arylboroxines under neutral conditions to give 3-arylpyrrolidines with high enantioselectivity in high yields.
- So, Chau Ming,Kume, Satoshi,Hayashi, Tamio
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supporting information
p. 10990 - 10993
(2013/08/23)
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- Palladium(II)-catalyzed enantioselective synthesis of α- (trifluoromethyl)arylmethylamines
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Trifluoromethylacetaldimines, generated in situ from the corresponding N,O-acetals, undergo 1,2-addition of arylboroxines under palladium(II) catalysis to generate a variety of α-(trifluoromethyl)arylmethylamines with good to high enantioselectivity (up to 97% ee). The pyridine-oxazolidine (PyOX) class of ligands was found to be particularly suitable for this transformation, which proceeds without exclusion of ambient air and moisture.
- Johnson, Thomas,Lautens, Mark
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supporting information
p. 4043 - 4045
(2013/09/12)
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- Palladium-catalyzed cascade reaction for the synthesis of substituted isoindolines
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Arylate then cyclize: A palladium(II)-catalyzed cascade sequence has been developed to provide highly diastereomerically enriched cis-1-aryl-3-vinyl isoindolines (see scheme). The method uses commercially available aryl boronic acids and boroxine compounds containing a variety of electron-rich, -neutral, or -poor aromatic groups. Ts=4-toluenesulfonyl. Copyright
- Williams, Florence J.,Jarvo, Elizabeth R.
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supporting information; experimental part
p. 4459 - 4462
(2011/06/26)
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- Nickel-catalyzed efficient and practical Suzuki-Miyaura coupling of alkenyl and aryl carbamates with aryl boroxines
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(Figure Presented) Suzuki-Miyaura coupling of unactivated alkenyl carbamates Is described to construct polysubstituted olefins. The developed process is also suitable for heteroaromatic and even electron-rich aromatic carbamates.
- Xu, Li,Li, Bi-Jie,Wu, Zhen-Hua,Lu, Xing-Yu,Guan, Bing-Tao,Wang, Bi-Qin,Zhao, Ke-Qing,Shi, Zhang-Jie
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supporting information; experimental part
p. 884 - 887
(2010/04/29)
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- Construction of polysubstituted olefins through Ni-Catalyzed direct activation of Alkenyl C-O of substituted alkenyl acetates
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(Figure Presented) Reliable companion: For the first time cross-coupling between alkenyl acetates and arylboroxines/PhZnCl has been developed via Ni catalysis. Alkenyl acetates could be well-differ-entiated from aryl acetates (see scheme). This reliable method provides a convenient pathway to construct polysubstituted styrene derivatives.
- Sun, Chang-Liang,Yang, Wang,Xiao, Zhou,Wu, Zhen-Hua,Li, Bi-Jie,Guan, Bing-Tao,Shi, Zhang-Jie
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supporting information; body text
p. 5844 - 5847
(2010/09/03)
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- Steric tuning of the amidomonophosphane-rhodium(l) catalyst in asymmetric addition of arylboroxines to n-phosphinoyl aldimines
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Highly enantioselective rhodium-catalyzed addition of arylboroxlnes to N-phosphinoylaldimines was realized by the steric tuning of a dlphenylphosphorus moiety to a di(o-tolyl)phosphorus moiety of a chiral amidomonophosphane. The presence of MS 4 A in a 5:1 solvent mixture of dioxane-propanol was essential to afford the corresponding dlarylmethylamines In high yield.
- Hao, Xinyu,Kuriyama, Masami,Chen, Qian,Yamamoto, Yasutomo,Yamada, Ken-Ichi,Tomioka, Kiyoshi
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body text
p. 4470 - 4473
(2009/12/24)
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- Synthetic and X-ray diffraction studies of borosiloxane cages [R′Si(ORBO)3SiR′] and the adducts of [ButSi{O(PhB)O}3SiBut] with pyridine or N,N,N′,N′-tetramethylethylenediamine
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Eleven borosiloxane [R′Si(ORBO)3SiR′] compounds where R′ = But and R = Ph (1), 4-PhC6H4 (2), 4-ButC6H4 (3), 3-NO2C6H4 (4), 4-CH(O)C6H4 (5), CpFeC5H4 (6), 4-C(O)CH3C6H4 (7), 4-ClC6H4 (8), 2,4-F2C6H3 (9), and R′ = cyclo-C6H11 and R = Ph (10), and 4-BrC6H4 (11) have been synthesized and characterized by spectroscopic (IR, NMR), mass spectrometric and, for compounds where R′ = But and R = 4-PhC6H4 (2), 4-ButC6H4 (3), 3-NO2C6H4 (4), CpFeC5H4 (6) and 2,4-F2C6H3 (9), X-ray diffraction studies. These compounds contain trigonal planar RBO2 and tetrahedral R′SiO3 units located around 11-atom "spherical" Si2O6B3 cores. The dimensions of the Si2O6B3 cores in compounds 2, 3, 4, 6 and 9 are remarkably similar. The reaction between [ButSi{O(PhB)O}3SiBut] (1), and excess pyridine yields the 1:1 adduct [ButSi{O(PhB)O}SiBut]. NC5H5 (12) while the reaction between 1 and N,N,N′,N′-tetramethylethylenediamine in equimolar amounts affords a 2:1 borosiloxane:amine adduct [ButSi{O(PhB)O}3SiBut]2 · Me2NCH2CH2NMe2 (13). Compounds 12 and 13 were characterised with IR and (1H, 13C and11B) NMR spectroscopies and the structure of the pyridine complex 12 was determined with X-ray techniques.
- Ferguson, George,Lawrence, Simon E.,Neville, Lorraine A.,O'Leary, Brian J.,Spalding, Trevor R.
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p. 2482 - 2492
(2008/10/09)
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