Most of the compounds have physiologically active properties, and their biological properties are often attributed to the heteroatoms contained in their molecules, and most of these heteroatoms also appear in cyclic structures. A Journal, European Journal of Organic Chemistry called Stabilized 2,3-pyridyne reactive intermediates of exceptional dienophilicity, Author is Connon, Stephen J.; Hegarty, Anthony F., which mentions a compound: 2402-95-1, SMILESS is ClC1=CC=CC=[N+]1[O-], Molecular C5H4ClNO, Computed Properties of C5H4ClNO.
The enhanced dienophilicity of 4-methoxy, 4-aryloxy and 4-thiophenoxy analogs of 2,3-pyridyne relative to itself is reported. The regioselective lithiation of 4-alkoxy- and 4-thiophenoxy-2-chloropyridine at low temperatures, followed by elimination of lithium chloride affords 4-alkoxy- and 4-thiophenoxypyridynes, which can be trapped in situ in a [4+2] cycloaddition reaction with furan to give endoxides in moderate to good yields (25-58%). In contrast, precursors with a hydrogen or Me substituent at C-4 give no evidence for pyridyne formation under these conditions. Attempts to generate 6-isopropoxy-2,3-pyridyne from the low-temperature lithiation of 2-chloro-6-isopropoxypyridine were unsuccessful due to the instability of the 2-chloro-6-isopropoxy-5-lithiopyridine.
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Reference:
Isoxazole – Wikipedia,
Isoxazole | C3H3NO – PubChem