7V-oxide

Few reports of successful 7V-oxide preparation have been found (48JCS1389, 71CR(C)-(273)1529), whilst other papers refer to many failures in attempted A( -oxidations, and the parent [2,3-f ] compound gives the 6-hydroxy derivative instead of an A( -oxide (63JCS5737). 

Compounds of this type are tautomeric in general, the 7V-oxide form (e.g. 570) is favored by polar media, the 7V-hydroxy form e.g. 569) by non-polar media. 

Azole 7V-oxide groups are readily removed by reduction with Zn/HOAc, HI or PCI3, e.g. in the pyrazole series. 1,2,3-Thiadiazole 3-oxides isomerize on irradiation to the corresponding 2-oxides. 

UV irradiation of 3-aminopyrido[4,3-e]-1,2,4-triazine 1-oxides 7 or 1,2,4-triazine 4-oxides 8 leads to deoxygenation, i.e., loss of the 7V-oxide function resulting in the corresponding 3-aminopyrido[4,3-e]-1,2,4-triazines 9 and 1,2,4-triazines 10 (76ACH327, 76LA153). At the same time, UV irradiation of the 1,2,4-triazine 4-oxides unsubstituted at the 5 position proceeds as a ring contraction to form triazoles 11 (76LA153). 

The cycloaddition reaction of 1,2,4-tiiazines 7V-oxides proceeds differently from the reaction of the corresponding 1,2,4-tiiazines. Thus the 1,2,4-triazine 4-oxide 55 acts only as a diene in the reaction with 1 -diethylaminopropyne to afford 2-methyl-4-(dimethylamino)pyrimidines 111. At the same time the 1,2,4-triazine 4-oxides 55 react with l-(dimethylamino)-l-ethoxyethylene by 1,3-dipolar cycloaddition to give 5-methyl-1,2,4-tiiazines 112 (78CB240). 

Benzazepines 1 are oxidized to their 7V-oxides 2 by 3-chloroperoxybenzoic acid (1 equivalent) at room temperature.78 1 78 However, at higher temperatures, and with an excess of oxidant,178 or with a stronger peracid.78 N-oxide formation is accompanied by epoxidation at C4-C5 (see Section 3.2.2.2.I.). 

Amino-2-dimethylainino-5-nitrosopyriinidin-4(3/0-one 36 reacts with dimethyl phenacylsulfonium bromides when refluxed in pyridine to give pteridinediones 37 rather than the isomeric 5-7V-oxides 38 < 96H(43)437 >. 

West and colleagues have reported the initial examples involving a N O/S O mixed donor ligand such as 2-(ethylsulphinyl)pyridine 7V-oxide for transition metal ion and lanthanide metal ion as shown in Scheme 22. Crystal field parameters based on... 

A convenient synthetic route to enantiomerically pure hydroxylated pyrroline-7V-oxides (108) has been reported (292). A key step is the formation of oo-oxo-enoates from D-ribose (107) and the subsequent 1,3-azaprotio cyclo-transfer reaction of the resulting oximino alkenoate derivatives (Scheme 2.43). 

Similarly, nitrones react with o.-R -allylthiols to give l,3-thiazolidine-7V-oxides (427). On heating, they are transformed into 1,5,2-oxathiazinanes (428) (Scheme 2.199) (685). 

Heteroindacenes have been prepared and studied by Hafner and co-workers.198 199 The syntheses of 1,3,5,7-tetra-te/t-butyl-4-azaindacene, its AA-oxide, and l,3,5,7-tetra-tot-butyl-4-phospha-s-indacenes have been recently reported (Scheme 66).200 The 12-jt-electron delocalized systems have been studied by dynamic NMR and X-ray and were subjected to molecular orbital calculations, and there is strong evidence of electron delocalization. However, X-ray crystallographic data for 4-phospha-s-indacene 164 and the 4-7V-oxide 164 show that there is a dual orientation in the crystal this disorder with two different orientations of the molecule does not allow for conclusions regarding bond lengths or delocalization, and the mediated structures show a D2h symmetry rather than C2h with localized double bonds. 

Formation of phenylhydronitroxide radicals, DMPO (5,5-dimethyl-l-pyrroline-7V-oxide)/glutathiyl and DMPO/hemoglobin thiyl free radical adducts has been detected in erythrocytes of rats in vivo after administration of nitrosobenzene and phenylhydroxylamine, respectively92,94. The data, however, could also be interpreted in a different way ... 

Acetylpyridine-3-carboxamide 7V-oxides were isolated as cyclic isomers 26B (R = /-Pr, r-Bu) in the solid state (87MI4). In CD3OD solution, the isopropyl derivative retains the cyclic structure, but for the /-butyl derivative a ring-chain equilibrium was observed Ky = 1.10 H-NMR). 

With pyridine 7V-oxides the situation is reversed in that amide ion reacts at the 4-position by the AE mechanism but at the 2-position by the EA mechanism, albeit in poor yield (Scheme 137) (67RTC655). 

Members of another class of powerful direct mutagens, four nitroazabenzo[a]pyrene derivatives, were identified by Sera and co-workers (1994) in the basic fraction of extracts of diesel exhaust and in ambient POM. Structures and direct mutagenic activities on strains TA98 and YG1024 (-S9 mix) of the 1- and 3-nitro-6-azabenzo[a]pyrenes and the 1- and 3-nitro-6-azabenzo[a]pyrene-7V-oxides are shown in Table 10.21 (Sera et al., 1992 Fukuhara et al., 1992). They have been measured in ambient air in Fukuoka, Japan, at concentrations of 1.1, 1.2, 0.8, and 0.3 ng/g, respec-... 

One of the conceptually appealing approaches for enantioselective PKR with cobalt-alkyne complexes is the use of chiral promoters. It is expected that a sterically biased promoter can approach to one of the two equivalent cobalts preferentially, and effect oxidation of GO to make a vacant coordination site. Early attempts were marginally successful, and there remained much room for improvement. Recently, enhanced enantioselectivity has been obtained by using a bulky amine A -oxides like brucine 7V-oxide 44 under carefully controlled conditions (Scheme... 

ChIoro-ort/7o-toluidine undergoes an initial metabolic activation step, probably via 7V-oxidation, to form a nitrosoarene that can bind covalently to haemoglobin. 

V-methylmorpholine 7V-oxide or 4-phenylpyridine TV-oxide as cocatalysts. The yields and enantioselectivities obtained with H2O2 or urea hydrogen peroxide were comparable, with slightly better yields for the epoxidation with H2O2 (73% versus 68% for the epoxide of 1,2-dihydronaphthalene in the presence of NH4OAC). 

Figure 11.6. SHMO orbitals and orbital energies for (a) pyrrole (b) pyridine (c) pyridinium (id) pyridine-7V-oxide (HOMO and LUMO only shown).

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