- Unusual Reactivity of 4-Vinyl Isoxazoles in the Copper-Mediated Synthesis of Pyridines, Employing DMSO as a One-Carbon Surrogate
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An efficient protocol for the synthesis of nicotinate derivatives and tetrasubstituted pyridines through a copper-mediated cleavage of isoxazoles has been developed. The highlight of the work is the observation of an unusual reactivity of 4-vinyl isoxazoles under the reaction conditions. DMSO serves as a one-carbon surrogate generating an active methylene group during the reaction to form two C-C bonds. This protocol provides a facile and an expeditious approach for the assembly of densely substituted N-heterocyclic compounds.
- Kumar, Pravin,Kapur, Manmohan
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p. 5855 - 5860
(2020/07/30)
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- Synthesis of 3,5-Disubstituted Isoxazoles through a 1,3-Dipolar Cycloaddition Reaction between Alkynes and Nitrile Oxides Generated from O-Silylated Hydroxamic Acids
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In this paper, we report the regioselective synthesis of 3,5-disubstituted isoxazoles by 1,3-dipolar cycloaddition between alkynyl dipolarophiles and nitrile oxide dipoles generated in-situ from O-silylated hydroxamic acids in the presence of trifluoromethanesulfonic anhydride and NEt3. Thanks to the mild, metal-free and oxidant-free conditions that this strategy offers, the reaction was successfully applied to a wide variety of alkynyl dipolarophiles, demonstrating the tolerance of this approach to diverse functional groups. In particular, we have shown that the method was compatible with biological molecules such as peptides and peptide nucleic acids (PNA). This protocol constitutes another example of metal-free 1,3-dipolar cycloaddition leading to the regioselective formation of isoxazoles.
- Carloni, Laure-Elie,Mohnani, Stefan,Bonifazi, Davide
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supporting information
p. 7322 - 7334
(2019/11/05)
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- Catalyst control in positional-selective C-H alkenylation of isoxazoles and a ruthenium-mediated assembly of trisubstituted pyrroles
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High levels of catalyst control are demonstrated in determining the positional selectivity in C-H alkenylation of isoxazoles. A cationic rhodium-mediated, strong-directing group promotes C(sp2)-H activation at the proximal aryl ring whereas, the palladium-mediated electrophilic metallation leads to the C(sp2)-H activation at the distal position of the directing group. Synthetic elaboration of this C-H alkenylation product via ruthenium and copper co-catalysis leads to an efficient method for the assembly of densely substituted pyrroles.
- Kumar, Pravin,Kapur, Manmohan
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p. 2134 - 2138
(2019/03/26)
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- Magtrieve (CrO2) and MnO2 mediated oxidation of aldoximes: Studying the reaction course
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Magtrieve (CrO2) and MnO2 mediated oxidation of aldoximes to nitrile oxides were studied in details. In presence of external radical source, TEMPO, these reagents did not furnish nitrile oxides, instead favoured deoximation to aldehydes. A common trend of deoximation was established from electronically tuned aldoximes, which is: aliphatic>aromatic> aldoximes with strong electron-withdrawing group, though the extent of deoximation was less in case of CrO2. Above effects were not observed with chloramine-T and diacetoxyiodobenzene, reagents known to produce nitrile oxides via hydroximoyl halide or equivalent ionic intermediates. A putative reaction mechanism is proposed for MO2 (M=Cr, Mn) mediated oxidation of aldoximes through formation of a nitroso-oxime tautomeric pair. Formation of nitrile oxide is possibly occurred from the oxime tautomer via a σ-type iminoxy radical intermediate. The deoximation process, dominating in presence of external radical environment, is explained following decomposition of the nitroso tautomer.
- Bhosale, Sandeep,Kurhade, Santosh,Vyas, Samir,Palle, Venkata P.,Bhuniya, Debnath
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scheme or table
p. 9582 - 9588
(2011/01/03)
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- Silyl isoxazolines-2: Synthesis, structure and properties
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Silyl isoxazolines have been synthesized by [2 + 3] cycloaddition reaction of nitrile oxides and silylnitronates to vinyl-and allylsilanes. The direction of the cycloaddition reaction of nitrile oxides to trialkoxyvinylsilanes has been shown to depend on
- Lukevics,Dirnens,Kemme,Popelis
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p. 235 - 244
(2007/10/03)
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- 1,3-Dipolar cycloaddition reaction of substituted trimethylstannylacetylenes with nitrile oxides
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1,3-Dipolar cycloaddition reaction of trimethylstannylacetylene with nitrile oxides yielded 3-substituted 5-(trimethylstannyl)isoxazoles. On the other hand, the same reaction of (trimethylstannyl)phenylacetylene, -1-hexyne, and -(trimethylsilyl)acetylene
- Sakamoto,Uchiyama,Kondo,Yamanaka
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p. 478 - 480
(2007/10/02)
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- Utilization of Vinylsilanes in Cycloaddition Reactions
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The reaction of several vinylsilanes with benzonitrile oxide, 2-diazopropane, C-carboethoxy-N-phenylnitrile imine, and substituted 1,3-butadienes has been examined.The 1,3-dipolar cycloadditions followed frontier orbital predictions and gave silylated iso
- Padwa, Albert,MacDonald, J. Gavin
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p. 3189 - 3195
(2007/10/02)
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- 1,3-DIPOLAR CYCLOADDITION OF BENZONITRILE OXIDE WITH VINYLSILANES
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The reaction of benzonitrile oxide with several vinylsilanes has been found to afford silylated isoxazoles.Relative rates for the cycloaddition reaction were determined.
- Padwa, Albert,MacDonald, J. Gavin
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p. 3219 - 3222
(2007/10/02)
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