- NMR spectrocopy of organolithium compounds, part XXXIV: Cyclopropyllithium and lithium bromide (1:1) in diethylether/tetrahydrofuran—Identification of a fluxional mixed tetramer
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Cyclopropyllithium, C3H5Li (1), was studied in the presence of one equivalent lithium bromide (LiBr) in diethylether (DEE)/tetrahydrofuran (THF) mixtures and in THF as solvents. Increasing the THF concentration in DEE/THF leads in the 6Li NMR spectrum to a main signal (S1) at δ0.85 (rel. to ext. LiBr/THF) and a second resonance (S2) at δ0.26 aside from a minor component at δ0.07. In pure THF, the ratio of these signals was 66: 28:6. 6Li and 13C NMR allowed to identify the main signal as belonging to a mixed dimer, 1?LiBr, and the signal at 0.26 ppm to a fluxional mixed tetramer, 12?(LiBr)2. 1J(13C,6Li) coupling constants of 11.0 and 9.8 Hz were measured at 168 K for S1 and S2, respectively, and chemical exchange between both signals was detected by 2D 6Li,6Li exchange spectroscopy and analyzed by temperature-dependent 1D 6Li line-shape calculations. These yielded the equilibrium constants Keq for the chemical exchange Li4(C3H5)2Br2 ? 2 Li2C3H5Br. Their temperature dependence leads to van't Hoff parameters of ΔH° = 4.6 kJ/mol, ΔS° = 41.4 J/mol K, and ΔG°298 = ?7.8 kJ/mol. From the rate constants k, Eyring parameters of ΔH* = 42.0 kJ/mol, ΔS* = 33.0 J/mol K, and ΔG* 298 = 32.2 kJ/mol were calculated for the forward reaction Li4(C3H5)2Br2 → 2 Li2C3H5Br and ΔH* = 37.5 kJ/mol, ΔS* = ?8.4 J/mol K, and ΔG* 238 = 40.0 kJ/mol for the reverse reaction 2Li2C3H5Br → Li4(C3H5)2Br2.
- Eppers, Oswald,Günther, Harald
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- Aldol-Tishchenko Reaction of α-Oxy Ketones: Diastereoselective Synthesis of 1,2,3-Triol Derivatives
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α-Oxy ketones, easily accessible by conventional routes, can be selectively deprotonated generating an enolate intermediate, which upon treatment with paraformaldehyde undergoes an aldol-Tishchenko reaction, leading to relevant 1,2,3-triol fragments in a totally diastereoselective manner. The excellent stereocontrol in the generation of a quaternary stereocenter is attributed to stereoelectronic effects in the Evans intermediate. This methodology allows overcoming some limitations of our previously reported strategy, based on the reaction of α-lithiobenzyl ethers with esters and paraformaldehyde, broadening the scope of the obtained polyols. Synthetic applications of this process include the preparation of a new dilignol model and some functionalized oxetanes.
- Sedano, Carlos,Virumbrales, Cintia,Suárez-Pantiga, Samuel,Sanz, Roberto
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supporting information
p. 3725 - 3734
(2021/07/02)
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- CONDENSED IMIDAZOLE DERIVATIVES SUBSTITUTED BY TERTIARY HYDROXY GROUPS AS PI3K-GAMMA INHIBITORS
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This application relates to compounds of Formula (I): or pharmaceutically acceptable salts thereof, which are inhibitors of PI3K-y which are useful for the treatment of disorders such as autoimmune diseases, cancer, cardiovascular diseases, and neurodegenerative diseases.
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Page/Page column 233
(2019/05/10)
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- Nickel-Catalyzed Cross-Coupling of Organolithium Reagents with (Hetero)Aryl Electrophiles
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Nickel-catalyzed selective cross-coupling of aromatic electrophiles (bromides, chlorides, fluorides and methyl ethers) with organolithium reagents is presented. The use of a commercially available nickel N-heterocyclic carbene (NHC) complex allows the reaction with a variety of (hetero)aryllithium compounds, including those prepared via metal-halogen exchange or direct metallation, whereas a commercially available electron-rich nickel-bisphosphine complex smoothly converts alkyllithium species into the corresponding coupled product. These reactions proceed rapidly (1 h) under mild conditions (room temperature) while avoiding the undesired formation of reduced or homocoupled products. Nickel-catalyzed cross-coupling of aromatic electrophiles with organolithium reagents is presented. The use of a commercially available nickel N-heterocyclic carbene complex allows reaction with a variety of (hetero)aryllithium compounds, whereas a commercially available electron-rich nickel bisphosphine complex smoothly converts alkyllithium species into the corresponding coupled product.
- Heijnen, Dorus,Gualtierotti, Jean-Baptiste,Hornillos, Valentín,Feringa, Ben L.
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supporting information
p. 3991 - 3995
(2016/03/16)
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- Glycomimetic replacements for hexoses and N-acetyl hexosamines
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Compounds and methods are provided for obtaining oligosaccharide mimics. More specifically, compounds and methods are described wherein oligosaccharide mimics are obtained by incorporating or substituting in a cyclohexane derivative.
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Page/Page column 24
(2008/12/06)
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- Transfer-dehydrogenation of alkanes catalyzed by rhodium(I) phosphine complexes
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Complexes of the form Rh(PMe3)2ClL' (L' = CO or trisubstituted phosphine) and [Rh(PMe3)2Cl]2 have previously been reported to catalyze the transfer-dehydrogenation of alkanes, using olefinic hydrogen acceptors under a dihydrogen atmosphere. Such complexes are herein reported to effect transfer-dehydrogenation in the absence of H2 but with much lower rates and total catalytic turnovers, even at much greater temperatures. Analogs with halides other than chloride (Br, I), or with pseudo-halides (OCN, N3), are found to exhibit generally similar behavior: high catalytic activity under H2 and measurable but much lower activity in the absence of H2. Thermolysis (under argon) of complexes [RhL2Cl]n (n = 1, 2; L is a phosphine bulkier than PMe3) in cyclooctane in the absence of hydrogen acceptors yielded cyclooctene. However, transfer-dehydrogenation was plagued by ligand decomposition. Under a hydrogen atmosphere complexes containing ligands much bulkier than PMe3 do not effect dehydrogenation. Complexes with tridentate ligands, η3-PXP)RhL' (PXP = (Me2PCH2Me2Si)2N, Me2PCH2(2,6-C6H3)CH2PMe2; L' = CO, C2H4), were also found to catalyze thermal or photochemical dehydrogenation of cyclooctane with limited reactivity. The structure of [Rh(PMe3)2Cl]2 was determined by single-crystal diffraction. The Rh(μ-Cl)2Rh bridge of 1 is folded like that of [Rh(CO)2Cl]2, unlike that of the planar PPh3 and PiPr3 analogs.
- Wang, Kun,Goldman, Martin E.,Emge, Thomas J.,Goldman, Alan S.
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