- Meta C-H Arylation of Electron-Rich Arenes: Reversing the Conventional Site Selectivity
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Controlling site selectivity of C-H activation without using a directing group remains a significant challenge. While Pd(II) catalysts modulated by a mutually repulsive pyridine-type ligand have been shown to favor the relatively electron-rich carbon centers of arenes, reversing the selectivity to favor palladation at the relatively electron-deficient positions has not been possible. Herein we report the first catalytic system that effectively performs meta C-H arylation of a variety of alkoxy aromatics including 2,3-dihydrobenzofuran and chromane with exclusive meta site selectivity, thus reversing the conventional site selectivity governed by native electronic effects. The identification of an effective ligand and modified norbornene (NBE-CO2Me), as well as taking advantage of the statistics, are essential for achieving the exclusive meta selectivity.
- Liu, Luo-Yan,Qiao, Jennifer X.,Yeung, Kap-Sun,Ewing, William R.,Yu, Jin-Quan
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supporting information
p. 14870 - 14877
(2019/10/02)
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- An efficient and chemoselective deprotection of aryl tert-butyldimethylsilyl (TBDMS) ethers by NaCN
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Phenolic tert-butyldimethylsilyl (TBDMS) ethers can be deprotected to yield phenols in excellent yield using sodium cyanide (NaCN) as catalyst in ethanol. The deprotectation of various phenolic TBDMS ethers were found to be very convenient, fast, high yielding and chemoselective.
- Qiao, Xue-Jun,Hou, Xiao,Fang, Wu-Hong,Bao, Xue-Fei,Chen, Guo-Liang
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p. 899 - 904
(2016/05/19)
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- Rapid assessment of protecting-group stability by using a robustness screen
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An experimentally simple method has been developed to rapidly establish the stability of widely utilized silyl, acetal, and carbamate protecting groups to a given set of reaction conditions. Assessment of up to twelve protecting groups in a single experiment has been demonstrated. Evaluation of this protocol in two unrelated synthetic transformations suggests that this method can be used to select appropriate protecting groups in the design of synthetic routes.
- Collins, Karl D.,Ruehling, Andreas,Lied, Fabian,Glorius, Frank
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supporting information
p. 3800 - 3805
(2014/04/03)
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- Metal-free synthesis of sterically crowded biphenyls by direct Ar-H substitution in alkyl benzenes
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(Chemical Equation Presented) Four's definitely a crowd: The chemoselective activation of Ar-H bonds in methylbenzenes by treatment with photogenerated phenyl cations allowed the synthesis of sterically crowded biphenyl compounds, including tetra-ortho-substituted biphenyls, by intermolecular cross-coupling (see scheme). This method is an appealing metal-free alternative to widely used transition-metal catalysis. TFE = 2,2,2-trifluoroethanol.
- Dichiarante, Valentina,Fagnoni, Maurizio,Albini, Angelo
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p. 6495 - 6498
(2008/09/16)
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- Tetrahydroisoquinoline LXR modulators
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A compound of formula I wherein X, R1, R2a, R3a, R3b, R4a, R4b, R4c and R5 are defined herein.
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Page/Page column 21
(2010/11/26)
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- benzamide derivatives as oxytocin agonists and vasopressin antagonists
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Novel compounds according to general formula 1, wherein G1 is NR5R6 or a fused polycyclic group that are specific OT receptor agonists and/or Via receptor antagonists. Pharmaceutical compositions comprising such compounds are useful in the treatment of, inter alia, primary dysmenorrhoea.
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- An Effective Approach for the Silylation of Hydroxyl Compounds in Room Temperature Ionic Liquids
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The room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6) is used as a "green" recyclable alternative to conventional solvents for the silylation of a series of hydroxyl compounds (alcohols and phenols
- Xu, Zhen-Yuan,Xu, Dan-Qian,Liu, Bao-You,Luo, Shu-Ping
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p. 4143 - 4149
(2007/10/03)
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- Facile methods for the direct conversions of aryl acetates into the corresponding methoxymethyl ethers or silyl ethers
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Direct conversion of aryl acetates into aryl methoxymethyl ethers or aryl trialkylsilyl ethers was readily accomplished by treatment with methoxymethyl bromide or trialkylsilyl trifluoromethanesulfonate, respectively, in the presence of sodium methoxide.
- Oriyama, Takeshi,Noda, Kojiro,Sugawara, Satomi
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p. 2217 - 2223
(2007/10/03)
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- Ring Expansion and Contraction of a Two-Carbon Bridged Spiropentane
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The reactions of tricyclo[4.1.0.01,3]heptan-4-one (5) and two related systems with diazomethane and m-CPBA were examined in order to determine the relative reactivity and migratory aptitudes for the three compounds. The reactions of 5 with diazomethane and m-CPBA yielded new derivatives of the tricyclo[5.1.0.01,3]octane ring system that showed that migration of cyclopropylcarbinyl is favored over cyclopropyl migration in this system. Photolysis of 5-diazotricyclo[4.1.0.01,3]heptan-4-one (23) in methanol and dimethylamine did not lead to ring contraction to the tricyclo[3.1.0.01,3]hexane ring system, but an interesting product was derived from an unusual rearrangement process in the photolysis in dimethylamine. Matrix photolysis of 23 at 15 K gave a decrease in the diazo band at 2085 cm-1 and the appearance of a new band at 2117 cm-1, which is a normal position expected for a small-ring ketene such as cyclopropylketene. Thus, matrix photolysis appears to have yielded a derivative of the previously unknown tricyclo[3.1.0.01,3]hexane ring system. The lithium enolate of 5 was characterized by NMR spectroscopy at -80 °C and was found to rearrange to m-cresol at -65 °C. The geometries of the bridged spiropentanes of this work were optimized at the MP2(frozen core)/6-31G* level of theory, and group equivalent values were derived in order to calculate the heats of formation for these compounds using the calculated energies.
- Wiberg, Kenneth B.,Snoonian, John R.
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p. 1390 - 1401
(2007/10/03)
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- PYRAN DERIVATIVES AND THEIR USE AS INHIBITORS OF 5-LIPOXYGENASE
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The invention concerns a cyclic ether derivative of the formula I, wherein Ar1 is optionally substituted phenyl, naphthyl or a 9-or 10-membered bicyclic heterocyclic moiety; A1 is a direct link to X1 or (l-3C)alkylene; X1 is oxy, thio, sulphinyl, sulphony
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