- Unexpected ring opening of pyrazolines with activated alkynes: synthesis of 1H-pyrazole-4,5-dicarboxylates and chromenopyrazolecarboxylates
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1H-Pyrazole-4,5-dicarboxylates and chromenopyrazole carboxylates were prepared by reacting pyrazolines with activated alkynes under neat conditions without a catalyst. The products were formed via unexpected ring opening of pyrazolines with the elimination of styrene/ethylene. These types of transformations are unknown and the products formed were confirmed using their spectral/analytical data. In addition, the structures of compounds 5e and 5n were confirmed by single-crystal X-ray analysis. Control experiments were conducted to support the proposed reaction mechanism.
- Bhimapaka, China Raju,Kolla, Sai Teja,Rayala, Nageswara Rao,Sridhar, Balasubramanian
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supporting information
p. 334 - 338
(2022/01/20)
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- TBHP/Cu(OAc)2 mediated oxidation of pyrazolines: A convenient method for the preparation of pyrazoles
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An efficient and simple oxidative protocol has been developed for the preparation of pyrazoles from pyrazolines mediated by TBHP/Cu(OAc)2 at room temperature. The present protocol has been successfully applied for the preparation of various pyrazole compounds from heterocyclic pyrazolines.
- Kolla, Sai Teja,Somanaboina, Ramya,Bhimapaka, China Raju
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supporting information
p. 1425 - 1432
(2021/02/27)
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- Ultrasound assisted synthesis of 1,5-diaryl and 1,3,5-triaryl-2-pyrazolines by using KOH/EtOH system with Cu(I) catalyst
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1,5-Diaryl-2-pyrazolines and 1,3,5-triaryl-2-pyrazolines were synthesized in alcoholic potassium hydroxide in high yields within 1-6 min under ultrasound irradiation at room temperature.
- Pise, Ashok S.,Jadhav, Sunil D.,Burungale, Arvind S.,Devkate, Santosh S.,Gawade, Ramesh B.
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p. 894 - 896
(2018/03/13)
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- Tris(pentafluorophenyl)borane-Catalyzed Acceptorless Dehydrogenation of N-Heterocycles
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Catalytic acceptorless dehydrogenation is an environmentally benign way to desaturate organic compounds. This process is traditionally accomplished with transition-metal-based catalysts. Herein, a borane-catalyzed, metal-free acceptorless dehydrogenation of saturated N-heterocycles is disclosed. Tris(pentafluorophenyl)borane was identified as a versatile catalyst, which afforded several synthetically important N-heteroarenes in up to quantitative yield. Specifically, the present metal-free catalytic system exhibited a uniquely high tolerance toward sulfur functionalities, and demonstrated superior reactivity in the synthesis of benzothiazoles compared to conventional metal-catalyzed systems. This protocol can thus be regarded as the first example of metal-free acceptorless dehydrogenation in synthetic organic chemistry.
- Kojima, Masahiro,Kanai, Motomu
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supporting information
p. 12224 - 12227
(2016/10/13)
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- Mechanism and Dynamics of Intramolecular C-H Insertion Reactions of 1-Aza-2-azoniaallene Salts
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The 1-aza-2-azoniaallene salts, generated from α-chloroazo compounds by treatment with halophilic Lewis acids, undergo intramolecular C-H amination reactions to form pyrazolines in good to excellent yields. This intramolecular amination occurs readily at both benzylic and tertiary aliphatic positions and proceeds at an enantioenriched chiral center with retention of stereochemistry. Competition experiments show that insertion occurs more readily at an electron-rich benzylic position than it does at an electron-deficient one. The C-H amination reaction occurs only with certain tethers connecting the heteroallene cation and the pendant aryl groups. With a longer tether or when the reaction is intermolecular, electrophilic aromatic substitution occurs instead of C-H amination. The mechanism and origins of stereospecificity and chemoselectivity were explored with density functional theory (B3LYP and M06-2X). The 1-aza-2-azoniaallene cation undergoes C-H amination through a hydride transfer transition state to form the N-H bond, and the subsequent C-N bond formation occurs spontaneously to generate the heterocyclic product. This concerted two-stage mechanism was shown by IRC and quasi-classical molecular dynamics trajectory studies. (Chemical Equation Presented).
- Hong, Xin,Bercovici, Daniel A.,Yang, Zhongyue,Al-Bataineh, Nezar,Srinivasan, Ramya,Dhakal, Ram C.,Houk,Brewer, Matthias
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p. 9100 - 9107
(2015/08/03)
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- Iron-catalyzed aerobic oxidative aromatization of 1,3,5-trisubstituted pyrazolines
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A simple and high yielding method for the synthesis of tri-substituted pyrazoles via iron(III) catalyzed aerobic oxidative aromatization of pyrazolines has been reported. The process demonstrates a variety of functional group tolerance.
- Ananthnag, Guddekoppa S.,Adhikari, Adithya,Balakrishna, Maravanji S.
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p. 240 - 243
(2013/12/04)
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- Stereospecific intramolecular C-H amination of 1-aza-2-azoniaallene salts
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We report that 1-aza-2-azoniaallene salts, generated from α-chloroazo compounds by treatment with halophilic Lewis acids, participate in intramolecular C-H amination reactions to provide pyrazoline products in good to excellent yield. This intramolecular amination occurs readily at both benzylic and tertiary aliphatic positions and proceeds at an enantioenriched chiral center without loss of enantiomeric excess. A competition reaction shows that insertion occurs more readily at an electron-rich benzylic position than an electron-deficient one. These observations are consistent with the 1-aza-2-azoniaallene intermediate reacting as a nitrenium-like ion by a concerted insertion mechanism.
- Bercovici, Daniel A.,Brewer, Matthias
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p. 9890 - 9893
(2012/08/08)
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- Synthesis of 1,3,5-trisubstituted pyrazolines via Zn(ii)-catalyzed double hydroamination of enynes with aryl hydrazines
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An efficient Zn(ii)-catalyzed intermolecular double hydroamination of 1,3-enynes with aryl hydrazines, for the synthesis of pyrazolines, has been discussed.
- Patil, Nitin T.,Singh, Vipender
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supporting information; experimental part
p. 11116 - 11118
(2011/11/29)
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- Catalytic asymmetric 6π-electrocyclization: Accessing highly substituted optically active 2-pyrazolines via diastereoselective alkylations
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The chiral phosphoric acid catalyzed asymmetric electrocyclization of α,β-unsaturated hydrazones has been studied. This reaction is one of the first catalytic asymmetric 6π-electrocyclizations reported, and enables the synthesis of 2-pyrazolines in high y
- Mueller, Steffen,List, Benjamin
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experimental part
p. 2171 - 2178
(2010/09/03)
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- Mechanically activated synthesis of 1,3,5-triaryl-2-pyrazolines by high speed ball milling
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An efficient mechanically activated solvent-free synthesis of 1,3,5-triaryl-2-pyrazolines from chalcones and phenylhydrazines using high speed ball milling is described. This method has notable advantages in terms of good yield, short reaction time and ne
- Zhu, Xingyi,Li, Zhenhua,Jin, Can,Xu, Li,Wu, Qianqian,Su, Weike
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experimental part
p. 163 - 165
(2010/04/22)
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- Solid-phase synthesis of pyrazolines and isoxazolines with sodium benzenesulfinate as a traceless linker
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(Matrix presented) The preparation of pyrazoline and isoxazoline derivatives with traceless solid-phase sulfone linker strategy is described. Key steps involved in the solid-phase synthetic procedure include (i) sulfinate S-alkylation, (ii) sulfone anion alkylation, (iii) γ-hydroxy sulfone → γ-ketosulfone oxidation, and (iv) traceless product release via elimination-cyclization. A library of 12 pyrazolines and isoxazolines was synthesized.
- Chen,Lam, Yulin,Lai, Yee-Hing
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p. 1067 - 1069
(2007/10/03)
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- 1,3-Dipolar Cycloadditions, 88. C-Methyl-N-phenylnitrilimine and the Regiochemistry of its Cycloadditions
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The title compound, a representative of the little known C-alkylnitrilimines, is accessible by three routes: NaNO2 elimination from sodium (α-nitroethylidene)phenylhydrazine in boiling acetonitrile, photolysis of 5-methyl-2-phenyltetrazole, and the thermo
- Fliege, Werner,Huisgen, Rolf,Clovis, James S.,Knupfer, Hans
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p. 3039 - 3061
(2007/10/02)
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