4-Nitropyridine A -oxide

Amine oxides, prepared to protect tertiary amines during methylation and to prevent their protonation in diazotized aminopyridines, can be cleaved by reduction (e.g., SO2/H2O, 1 h, 22°, 63% yield H2/Pd-C, AcOH, AC2O, 7 h, 91% yield Zn/HCl, 30% yield). Photolytic reduction of an aromatic amine oxide has been reported [i.e., 4-nitropyridine A-oxide, 300 nm, (MeO)3PO/CH2Cl2, 15 min, 85-95% yieldl. ... 

Acylation with acetyl chloride (giving 94) or protonation permits rapid displacement of the nitro group from 4-nitropyridine A-oxide by the weakly nucleophilic chloride Pyridine A-oxide... 

The crystal structures of [Ag(l,4-dioxane)]AsF69 9 and [Ag2(l,4-oxathiane)](N03)295° have been reported. Two adducts of the 4-nitropyridine A-oxide with silver nitrate have been characterized, one is a mononuclear tetracoordinated compound [Ag(N03)(0NC5H4N02)2] and the other is a dinuclear pentacoordinated species [Ag2(N03)2(/u-0NC5H4N02)2(0NC5H4N02)2] (130).951,952 In the mixed compound /nmv-[RhCl2(py)4]N03-AgN03 exists the dinitroargentate(I) ion in a distorted tetrahedral environment 953... 

In nitroamine oxides the nitro group may be reduced preferentially but usually both functions are affected. 5-Ethyl-2-methyl-4-nitropyridine A -oxide is converted quantitatively to 4-amino-5-ethyl-2-methylpyridine by hydrogen over 30% palladium on charcoal in ethanolic solution [737]. The outcome of the hydrogenation of a nitroamine oxide may be influenced by reaction conditions [736]. 

A-Nitroamino)pyridine A-oxide, 1852 2,2 -bipyridyl 1-oxide, 3258 4-Nitropyridine A-oxide, 1833 2,2 -Oxybis(iminomethylfiu an) mono-A-oxide, 3260 Pyridine A-oxide, 1849... 

Having established that the end game of the proposed synthesis of cylindrospermopsin (1) from bromoketone 4 was viable, we turned our attention to the preparation of acetylene 5 from 4-methoxy-3-methylpyridine (7). 4-Methoxy-3-methylpyridine (7) was prepared by modifications of the literature procedure.17,18 3-Methyl-4-nitropyridine A-oxide (27),19 was treated with K2CO3 in methanol at 70 °C to displace the nitro group to... 

Methyl-4-nitropyridine A -oxide, 2310 2-Methyl-5-nitrobenzenesulfonic acid, 2768 Methylborylene, 0424 Methylnitrothiophene, 1844... 

As has already been mentioned in Section II, pyridine A-oxide is much more susceptible to electrophilic attack than is pyridine. Nitration with fuming nitric acid in sulfuric acid at 90° or with potassium nitrate or nitric acid in fuming sulfuric acid at 100-130° gives up to 90% yields of 4-nitropyridine A-oxide together with a small amount of the 2-isomer (formation of 2-isomer reported by... 

To 50.0 g (0.36 mol) of 4-nitropyridine A -oxide in 360 mL of methanol 50 g (0.5 mol) of potassium carbonate were added and the mixture was stirred at reflux for 8 h. After cooling to room temperature the solution was filtered and the solvent removed under reduced pressure. The residue was treated five times with 100 mL of dichloromethane. After rota-evaporation of the dichloromethane 35.8 g (92%) of a white crystalline solid was obtained, mp 78 - 79 °C, Rf = 0.39 (chloroform/methanol 4 1 on silica gel). 

As yet, however, no reactive nitro-N-heterocycle, such as 5-nitropyri-midine (325), l-alkyl-5-nitropyrimidine-2-one, or 4-nitropyridine-A-oxide [or N-heterocycles containing other acceptor groups such as 2-methylsulfonylpyrimidine (265) or 3-methylsulfonyl-l, 2,4-triazine (267)] have been aminated using this interesting new procedure. 

Preparation of the 2-chloro-3-methoxy-4-nitropyridine A -oxide intermediate in the synthesis was considerably improved by the methylation of commercially available 2-chloro-3-pyridinol using dimethylsulfate and tet-rabutylammonium bromide as the catalyst under phase-transfer conditions (370), instead of diazomethane (Scheme 48). In the synthesis of orellanines elaborated by Tiecco et al. (299,301,309), shown in Scheme 49, the commercially available 3-hydroxypyridine was the starting material. The structures of the synthetic compounds were proved to be identical to those... 

Nitropyridine and 4-nitropyridine A-oxide have been shown to react with iso-prene, 1-methoxy-l,3-butadiene, and Danishefsky s diene to produce isoquinoline cycloadducts. One asymmetric and asynchronous transition state (TS) was detected between the reactants and the cycloadduct with isoprene and two TS were observed when 1-methoxy-l,3-butadiene and Danishefsky s diene were used. The Diels-Alder reaction of highly substituted dihydropyridines with e-deficient alkenes produced highly substituted isoquinuclidines with high stereo- and regio-selectivity. The Diels-Alder cycloaddition of cyclopentadiene to lithium ion encapsulated [60]fullerene proceeds at a higher rate than with that of empty [60]fullerene. ... 

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