Categories: C=N Bond Formation >
Synthesis of nitrones
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Simple thermal conditions, previously found to minimize hydroxylamine
decomposition (t-BuOH, 110 °C), allow the condensation of ketones and
hydroxylamines to form exocyclic, acyclic, and α,β-unsaturated ketonitrones with
benzylic, linear, and branched nitrogen substituents in modest to excellent
isolated.
J. Y. Pfeiffer A. M. Beauchemin, J. Org. Chem., 2009,
74, 8381-8383.
The reaction of N-alkylhydroxylamines and aqueous
hydroxylamine with monosubstituted allenes gives nitrones and oximes,
respectively,
in good yields. DFT calculations support a
proposed concerted, five-membered Cope-type hydroamination process, and calculated
transition state energies are in excellent agreement with experimental
observations.
J. Moran, J. Y. Pfeiffer, S. I. Gorelsky, A. M. Beauchemin, Org. Lett., 2009,
11, 1895-1898.
A general, efficient and metal-free protocol for the direct oxidation of
secondary amines to nitrones tolerates other functional groups or existing
stereogenic centers using Oxone in a biphasic basic medium as the sole oxidant.
C. Gella, È. Ferrer, R. Alibés, F. Busqué, P. de March, M. Figueredo, J. Font, J. Org. Chem., 2009,
74, 6365-6367.
An Ir-catalyzed reductive formation of functionalized nitrones from N-hydroxyamides
via dehydrosilylation and hydrosilylation showed high chemoselectivity in the
presence of sensitive functional groups, such as methyl esters. The reaction was
successfully applied to the synthesis of cyclic and macrocyclic nitrones, which
are known to be challenging compounds.
S. Katahara, S. Kobayashi, K. Fujita, T. Matsumoto, T. Sato, N. Chida, J. Am. Chem. Soc., 2016,
138, 5246-5249.
A direct coupling of N-nosylhydrazones with nitrosoarenes enables an
efficient and transition-metal-free synthesis of (Z)-N-arylnitrones
under mild conditions. The protocol is compatible with a wide range of
functional groups and provides the corresponding nitrones in very good yields by
a simple recrystallization process.
T. Liu, Z. Liu, Z. Liu, D. Hu, Y. Wang, Synthesis, 2018, 50,
1728-1736.
Cu catalysis enables the synthesis of N-alkylated unsaturated
ketonitrones from propargyloxyamines. The rearrangement reaction proceeds via
Cu-catalyzed intramolecular hydroamination, followed by thermally induced
electrocyclic ring opening.
I. Nakamura, T. Onuma, R. Kanazawa, Y. Nishigai, M. Terada, Org. Lett.,
2014,
16, 4198-4200.
Solvothermal treatment of magnesium iodide (MgI2) with sodium
hydride (NaH) provides magnesium hydride (MgH2), which can be used
for hydromagnesiation of 1,3-enynes. Downstream functionalization of the
resulting propargylmagnesium intermediates with organo nitro compounds affords
α-alkynylnitrones.
Y. Li, J. S. Ng, B. Wang, S. Chiba, Org. Lett., 2021, 23,
5028-5032.
4-Dimethylaminopyridine (DMAP) catalyzes a single-step preparation of
nitrones from benzyl halides and nitrosoarenes under mild reaction conditions.
The reaction provides both keto- and aldonitrones in good yields. As an
application of the reaction, methyl 2-bromo-2-phenylacetate was used to prepare
the corresponding isoxazolidine by a sequential one-pot synthesis.
Y. Jung, J. E. Hong, J.-H. Kwak, Y. Park, J. Org. Chem., 2021, 86,
6343-6350.
Oxidations of organic substrates such as sulfides, secondary amines, N-hydroxylamines,
and tertiary amines with molecular oxygen in the presence of
5-ethyl-3-methyllumiflavinium perchlorate catalyst and hydrazine monohydrate
in 2,2,2-trifluoroethanol occur highly efficiently to give the corresponding
oxidized compounds in excellent yields.
Y. Imada, H. Iida, S. Ono, S.-I. Murahashi, J. Am. Chem. Soc., 2003, 125, 2868-2869.