In general, if the atoms that make up the ring contain heteroatoms, such rings become heterocycles, and organic compounds containing heterocycles are called heterocyclic compounds. An article called Marked changes in relative nucleophilic strength in comparing SN reactions of some heterocyclic and homocyclic aromatic systems, published in 1983-07-31, which mentions a compound: 2402-95-1, Name is 2-Chloropyridine 1-oxide, Molecular C5H4ClNO, Related Products of 2402-95-1.
The kinetics of the nucleophilic substitution reactions of 2- and 4-chloropyridine 1-oxides (I and II, resp.) and 3,6-dichloropyridazine (III) with MeO- and PhS- in MeOH were determined Comparison of the results with those previously reported for 2,4-(O2N)2C6H3R (R = Cl, iodo) (IV and V, resp.), showed a marked change in the relative nucleophilicity of MeO- and PhS- and PhS- in MeOH. At 0° the PhS-/MeO- rate ratios for IV and V were 1.95 × 103 and 1.68 × 104, resp., whereas for I, II and III they were 5.03, 4.87 and 0.538, resp. These results are discussed in terms of retention of the arenide electrons in the heterocyclic ring.
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Reference:
Isoxazole – Wikipedia,
Isoxazole | C3H3NO – PubChem