- Asymmetric o-to-c aryloxycarbonyl migration of indolyl carbonates using single-handed dynamic helical polyquinoxalines bearing 4-aminopyridyl groups as chiral nucleophilic catalysts
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Use of single-handed dynamic helical macromolecules as nucleophilic catalysts in asymmetric Steglich-type O-to-C aryloxycarbonyl rearrangement of 3-substituted indol-2-yl aryl carbonates is demonstrated. Among several single-handed poly-(quinoxaline-2,3-diyl) copolymers (PQXap) bearing achiral 4-aminopyridin-3-yl groups at the 5-position of the quinoxaline rings, PQXmdpp and PQXapy, containing N-methylpyrrolidine-fused pyridin-3-yl and 4-(1-azetidinyl)pyridin-3-yl groups, respectively, showed higher enantioselectivity and catalytic activity than PQXdmap, bearing 4-dimethylamino-pyridine-3-yl groups. Substrates bearing p-(trifluoromethyl)phenyloxycarbonyl groups on both the nitrogen and oxygen atoms showed high reactivity, giving oxindoles with a quaternary stereogenic carbon center at their 3-positions in up to 97:3 enantiomeric ratio in THF. The macromolecular catalysts underwent inversion of their helix sense by solvent effect, allowing the same catalyst to give the opposite enantiomer in a mixture of methyl t-butyl ether and 1,1,2-trichloroethane (3:1). The macromolecular catalysts could be easily recovered by adding acetonitrile to the reaction mixture and were reused four times without reduction in enantioselectivity.
- Yamamoto, Takeshi,Takahashi, Takuya,Murakami, Ryo,Ariki, Naoto,Suginome, Michinori
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supporting information
p. 943 - 949
(2021/04/29)
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- Versatile Cp*Co(III)(LX) Catalyst System for Selective Intramolecular C-H Amidation Reactions
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Herein, we report the development of a tailored cobalt catalyst system of Cp*Co(III)(LX) toward intramolecular C-H nitrene insertion of azidoformates to afford cyclic carbamates. The cobalt complexes were easy to prepare and bench-stable, thus offering a convenient reaction protocol. The catalytic reactivity was significantly improved by the electronic tuning of the bidentate LX ligands, and the observed regioselectivity was rationalized by the conformational analysis and DFT calculations of the transition states. The superior performance of the newly developed cobalt catalyst system could be broadly applied to both C(sp2)-H and C(sp3)-H carbamation reactions under mild conditions.
- Chang, Sukbok,Jung, Hoimin,Kim, Dongwook,Lee, Jeonghyo,Lee, Jia,Park, Juhyeon
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supporting information
p. 12324 - 12332
(2020/08/06)
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- β-type glycosidic bond formation by palladium-catalyzed decarboxylative allylation
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The efficient and stereoselective construction of glycosidic linkages is of great significance in carbohydrate chemistry due to the ubiquitous existence of numerous biologically active natural products and saccharides. Although great efforts have been devoted to stereoselective glycosylations in the past few decades, constructing glycosidic bonds with high efficiency and selectivity remains a challenge and continues to be an important area in carbohydrate research. Phenols are widely used as nucleophiles in palladium-catalyzed allylation. In contrast, the possibility of using aliphatic alcohols as nucleophiles is not as thoroughly explored. The modified reaction conditions were then applied to other substrates. Originating from easily prepared carbonates, various glycosides, such as phenolic Oglycosides, thiophenolic S-glycoside, aliphatic O-glycosides, and even disaccharides, were synthesized in good yields by means of a palladium-catalyzed decarboxylative allylation.
- Xiang, Shaohua,Lu, Zhiqiang,He, Jingxi,Hoang, Kim Le Mai,Zeng, Jing,Liu, Xue-Wei
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supporting information
p. 14047 - 14051
(2013/11/19)
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- New N-arachidonoylserotonin analogues with potential "dual" mechanism of action against pain
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N-Arachidonoylserotonin (AA-5-HT, 1a) is an inhibitor of fatty acid amide hydrolase (FAAH) that acts also as an antagonist of transient receptor potential vanilloid-type 1 (TRPV1) channels and is analgesic in rodents. We modified the chemical structure of 1a with the aim of developing "hybrid" FAAH/TRPV1 blockers more potent than the parent compound or obtaining analogues with single activity at either of the two targets to study the mechanism of the analgesic action of 1a. Thirty-eight AA-5-HT analogues, containing a serotonin "head" bound to a variety of lipophilic moieties via amide, urea, or carbamate functionalities, were synthesized. Unlike 1a, most of the new compounds possessed activity at only one of the two considered targets. The amides 1b and 1c of α- and γ-linolenic acid, however, showed "hybrid" activity similar to 1a. The carbamate 3f (OMDM106), although unable to antagonize TRPV1 receptors, was the most potent FAAH inhibitor in this study (IC50 = 0.5 μM). Compounds 3f and 1m (OMDM129), which exhibited activity at only FAAH or TRPV1, respectively, were 10-fold less potent than 1a at preventing formalin-induced hyperalgesia in mice.
- Ortar, Giorgio,Cascio, Maria Grazia,De Petrocellis, Luciano,Morera, Enrico,Rossi, Francesca,Schiano-Moriello, Aniello,Nalli, Marianna,De Novellis, Vito,Woodward, David F.,Maione, Sabatino,Di Marzo, Vincenzo
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p. 6554 - 6569
(2008/09/17)
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- Synthesis of polyalkylphenyl prop-2-ynoates and their flash vacuum pyrolysis to polyalkylcyclohepta[b]furan-2(2H)-ones
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A new method for the smooth and highly efficient preparation of polyalkylated aryl propiolates has been developed. It is based on the formation of the corresponding aryl carbonochloridates (cf Scheme 1 and Table 1) that react with sodium (or lithium) propiolate in THF at 25-65°, with intermediate generation of the mixed anhydrides of the arylcarbonic acids and prop-2-ynoic acid, which then decompose almost quantitatively into CO2 and the aryl propiolates (cf. Scheme 11). This procedure is superior to the transformation of propynoic acid into its difficult-to-handle acid chloride, which is then reacted with sodium (or lithium) arenolates. A number of the polyalkylated aryl propiolates were subjected to flash vacuum pyrolysis (FVP) at 600-650°and 10-2 Torr which led to the formation of the corresponding cyclohepta[b]furan-2(2H)-ones in average yields of 25-45% (cf. Scheme 14). It has further been found in pilot experiments that the polyalkylated cyclohepta[b]furan-2(2H)-ones react with 1-(pyrrolidin-1-yl)cyclohexene in toluene at 120-130°to yield the corresponding 1,2,3,4- tetrahydrobenz[a]azulenes, which become, with the growing number of Me groups at the seven-membered ring, more and more sensitive to oxidative destruction by air (cf. Scheme 15).
- Nagel, Matthias,Hansen, Hans-Juergen
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p. 1022 - 1048
(2007/10/03)
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- Process for the preparation of chloroformic acid aryl esters
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In a process for the preparation of an aromatic chloroformic acid ester by contacting a phenol and phosgene, the improvement wherein the reaction is carried out in a homogeneous liquid phase at a temperature of 60° to 180° C. in the presence of organic phosphorus compound of the formula in which R1, R2 and R3 independently of one another represent hydrogen, alkyl, alkenyl, aralkyl, aryl or halogen and two of the said radicals together with the phosphorus atom can form a 5-membered or 6-membered phosphorus-containing saturated or unsaturated heterocyclic radical, X represents OH, homopolar-bonded halogen or an inorganic or organic acid anion, R4 denotes hydrogen or alkyl or, if X denotes halogen, can also denote halogen and n denotes 0 or 1, and in which, furthermore, R4 and X together can represent oxygen or sulfur.
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