Heterocycle N-oxides

POLONOVSKY N-oxide Rearrangement Conversion of heterocyclic N-oxIdes to a-acetoxyheterocycles... 

These compounds show the typical reactions of heterocyclic N-oxides and their structure was proved by methylation which takes place on N-1. Quinazoline 3-oxide is soluble in water and melts at 155°C. It has basic properties and its pKa value in water is 1.47. ... 

A. R. Katritzky and J. M. Lagowski, Chemisty of Heterocyclic N-Oxides. Academic Press, New York, 1971. 

Reactions of Heterocyclic N-Oxides with Trimethylsilyl Cyanide, Trimethylsilyl Azide, Trimethylsilyl Isothiocyanate, and Trimethylsilyl Halides... 

Heterocyclic N-oxides such as pyridine, quinoline, or isoquinoline N-oxides can be converted into a mixture of 2- and some 4-cyanopyridines, 2- or 4-cyanoquino-lines, or 1-cyanoisoquinolines, in 40-70% yield, in a Reissert-Henze reaction, by activation of the N-oxide function by O-acylation [1] or O-alkylation [2, 3] followed by treatment with aqueous alkali metal cyanide in H2O or dioxane. 

Alternatively, unreactive heterocyclic N-oxides might also be readily converted into their a-cyano heterocycles on reaction with the strongly electrophilic Cl3SiCN, Cl2Si(CN)2, or ClSi(CN)3, which should be formed in situ on addition of SiCl4 to a solution or suspension of sodium or potassium cyanide in acetonitrile or DMF (cf the analogous formation of ClSi(N3)3 708 in Scheme 5.70). 

Additions of Allyl- and Benzy/hrimethykiianes to Aromatic Heterocyclic N-Oxides 1159... 

A Reductions of Heterocyclic N-Oxides and Aromatic Nitro Groups 1165... 

As already discussed in Section 7.4, hexamethyidisiiane 857 (which is produced on a technical scale), in the presence of catalytic amounts of tetrabutylammonium fluoride di- or trihydrate in THF, reduces aromatic heterocyclic N-oxides such as pyridine N-oxide 860, quinoline N-oxide 877, or isoquinoline N-oxide 879 to the heterocycles [95] and nitrones to Schiff-bases. Aromatic nitro compounds such as nitrobenzene are reduced analogously to azo compounds such as azobenzene [96]. As mentioned in Section 7.5, secondary aliphatic nitro groups are reduced to oximes. 

Albini A, Pietra A (1991) Heterocyclic N-oxides. CRC Press, Boston... 

Other heterocyclic N-oxides have been found to display biological activities that may depend on their proven or hypothesised ability to release NO these include 4/ /-pyrazol-4-oTie 1,2-dioxides 71, 2H-1,2,3-triazole 1-oxides 72, benzotetrazine 1,3-dioxides 73 and 1,2,3-benzotriazine 3-oxides 74. These systems have been less extensively studied than the furoxan and 1,2-diazetine dioxide systems discussed above. 

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