Nitrones reagents

Notes. (1) Prepare the nitron reagent by dissolving 3.75 g nitron in 25 mL 5 per cent acetic (ethanoic) acid (by volume). Store in a dark bottle. 

The intermolecular cycloaddition route to spirocyclopropyl isoxazolidines and their subsequent rearrangement, used so widely by Brandi and co-workers (372-375) (Schemes 1.16 and 1.17, Section 1.5), has also been achieved in an intramolecular sense (Scheme 1.72). Cycloaddition of the alkenyl nitrone reagents (333a-c) afforded bicyclic isoxazolidinyl adducts 334, which rearranged under thermolysis in analogous fashion to the earlier work to give piperidinones (335) via... 

Similarly, variously substituted 3-imidazoline nitrone reagents and the related nitroxides (363 R = O) are popular targets and have demonstrated their reactivity toward various dipolarophiles, (e.g., styrene. Scheme 1.80) (420-431). However, only one group reports the use of a 2-imidazoline nitrone (432 34), which has demonstrated complete diastereofacial selectivity in its reactions with electron-... 

Special test 1. Add iron (II) sulfate, shake, and then add concentrated sulfuric acid produces brown ring 2. White precipitate is formed upon addition of nitron reagent (C20H16N4) test is not specific to only nitrates, however see table of precipitation reagents... 

Nitron reagent (diphenyl-endo-anilo-dihyd.rotriazole C2qH16Na)... 

Nitron reagent (5%). Dissolve 5 g nitron (C20H16N4) in 100 ml 2m acetic acid. 

Determination of the nitrate group attached to a primary carbon atom depends on its unique replacement by iodine on interaction with sodium iodide. This method was successfully used for measuring the proportion of substitution at C6 of partially nitrated cellulose. An approximate estimate of the labile nitrate on Cl of aldoses is made by boiling the compound with barium carbonate in methanol and determining the liberated nitrate ion with the Nitron reagent. 

Chiral nitrone reagents for cycloaddition reactions 00JEIC481. 

Nitrones are among the most highly studied and useful reagents for the synthesis of five-membered-nng heterocycles. The first fluonnated nitrone, N-methyl-C-(trifluoromethyl)nitrone, was prepared recently and used to introduce Irifluoromethyl groups into such heterocycles... 

The use of chiral dipolarophiles, such as the nitrile oxide additions to chiral furanones, have received much interest. The cycloaddition of various 1,3-dipolar reagents to the enantiomeric ally pure furanones 170 and 227 showed excellent diastereofacial control by the menthyloxy substituent, especially in nitrone and nitrile oxide additions (cf. Table II) (88TL5317). 

Nitron is a yellow, crystalline solid, m.p. 189 °C, which is insoluble in water. The reagent consists of a 10 per cent solution in 5 per cent acetic add it should be filtered, if necessary, and the clear solution protected from light. 

Note. Prepare the reagent by dissolving 5 g of nitron in 50 mL of 5 per cent acetic acid. Store in an amber bottle. 

Table 6. Addition of Organometallic Reagents to Racemic Nitrones S8-9...

The diastereoselectivity of the nucleophilic addition to nitrone 2 may be rationalized by assuming that magnesium bromide preferentially coordinates with the nitrone oxygen. The Grignard reagent is therefore forced to interact with the acetal oxygen in position 3. 

Michael addition of alkyl organometallic reagents to a,/ -disubstituted nitroalkenes followed by protonation of the intermediate nitronate anion generally gives mixtures of syn- and anti-diastereomers with poor diastereoselectivity19. 

NC Nitromannitol etc and can serve as a gravimetric reagent. The Nitron method for the detn of N is based on the fact that it ppts inorganic nitrates from w soln, and forms an insol addition product, C20H16N4.HNO3, mw 375.3... 

Oximes can be alkylated by alkyl halides or sulfates. N-Alkylation is a side reaction, yielding a nitrone. " The relative yield of oxime ether and nitrone depends on the nature of the reagents, including the configuration of the oxime, and on the reaction conditions. For example, anri-benzaldoximes give nitrones, while the syn isomers give oxime ethers. " ... 

Similar workup conditions applied to the nitronate arising from 1,4-addition of unsaturated Grignard or Li reagents 80 (M = MgBr provided better yields) to P Ar or jS-hetero-Ar nitro alkenes 79 provided isoxazolines 82 in a practically one pot reaction sequence (Eq. 8, Table 7) [33]. 

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