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Pure Appl. Chem.
75(10), 1403-1415, 2003
Pure and Applied Chemistry
Vol. 75, Issue 10
Nitropyridines: Synthesis and reactions*
Department of Chemistry, Norwegian University of Science
and Technology, N-7491 Trondheim, Norway
Abstract: Reaction of pyridine and substituted pyridines with
N2O5 in an organic solvent gives the N-nitropyridinium
ion. When this is reacted with SO2/HSO3–
in water, 3-nitropyridine is obtained (77 % yield). With substituted
pyridines, the method gives good yields for 4-substituted and moderate
yields for 3-substituted pyridines. The reaction mechanism is not an
electrophilic aromatic substitution, but one in which the nitro group
migrates from the 1-position to the 3-position by a [1,5 ] sigmatropic
shift. From 4-aminopyridine, imi- dazo [4,5-c ] pyridines have
been synthesized. From 3-nitropyridine, 5-nitropyridine-2-sulfonic acid
is formed in a two-step reaction. From this, a series of 2-substituted-5-nitro-pyridines
has been synthesized. 3-Nitropyridine and 4-substituted-3-nitropyridines
have been substituted with ammonia and amines by the vicarious substitution
method and by the oxidative substitution method in the position para
to the nitro group. High regioselectivities and yields have been obtained
in both cases to afford a series of 4-substituted-2-alkylamino-5-nitropyridines.
*Lecture presented at the 4th Florida Heterocyclic
Conference, Gainesville, Florida, 10-12 March 2003. Other presentations
are published in this issue, pp. 1403-1475.
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