Oxime, formation

Diels-Alder reaction of 2-bromoacrolein and 5-[(ben2yloxy)meth5i]cyclopentadiene in the presence of 5 mol % of the catalyst (35) afforded the adduct (36) in 83—85% yield, 95 5 exo/endo ratio, and greater than 96 4 enantioselectivity. Treatment of the aldehyde (36) with aqueous hydroxylamine, led to oxime formation and bromide solvolysis. Tosylation and elimination to the cyanohydrin followed by basic hydrolysis gave (24). 

Dimethyl ketals and enol ethers are stable to the conditions of oxime formation (hydroxylamine acetate or hydroxylamine hydrochloride-pyridine). Thioketals and hemithioketals are cleaved to the parent ketones by cadmium carbonate and mercuric chloride. Desulfurization of thioketals with Raney nickel leads to the corresponding methylene compounds, while thioenol ethers give the corresponding olefin. In contrast, desulfurization of hemithioketals regenerates the parent ketone. ... 

A mixture of 3 -hydroxypregna-5,l6-dien-20-one acetate (10 g), 70 ml of ethanol and 2 ml of methoxylamine is refluxed for 12 hr (Note methoxyl-amine hydrochloride leads to oxime formation). After cooling, another 1.75 ml of methoxylamine is added and the reaction is refluxed for another 12 hr. The solvent is removed in vacuo and the residue is dissolved in ether. Hydrogen chloride gas is passed into the ether solution and the white crystalline salt (113) is filtered off and washed with ether (85% yield crude mp 228-229°). 

Langer and coworkers constructed diverse O- and N-heterocydic scaffolds, such as y-alkylidene-a-hydroxybutenolides and pyrrolo[3,2-b]pyrrol-2,5-diones, exploiting the well-established cyclization strategy of bisnucleophiles with oxalic acid derivatives [163], while Stockman s research group reported in this context on a novel oxime formation/Michael addition providing the structural core of the alkaloid perhydrohistrionicotoxin [164]. 

Amongst other N-nucleophilic species, hydroxylamine exhibits some abnormal behavior besides oxime formation (p. 25). Thus it reacts with diphenyl cyclopropenone42 probably by 1,4-addition and subsequent oxidation and/or decarboxylation giving rise to 3,4-diphenyl isoxazolone (328) and desoxybenzoin oxime. With pentyl cyclopropenone48 hydroxylamine undergoes addition followed by normal oxima-tfon after ring fission yielding 2,3-dioximino octane (329). 

Quinone dyes, 9 503 Quinone ketals, anodic oxidation of hydroquinone ethers to, 21 264 Quinone methides, 2 209-211 Quinone Michael addition chemistry, 21 248-249, 250, 252 Quinone monoacetals, 21 251 Quinone monoimine (QMI), 19 246 Quinone oximes, formation of,... 

The reduction of aliphatic nitrocompounds in acid solution proceeds in two steps. First the nitrosocompound is formed. A low steady state concen ation of 2-methyl-2-nitrosopropane has been detected during the reduction of 2-methyl-2-nitropropane [13]. At the cathode potential necessary to attach the first electron to a nitro group, the nitroso intermediate undergoes further reduction to the hydroxyla-mine. When the nitrocompound has one a-hydrogen substituent, tautomerism of the nitroso intermediate to an oxime is in competition with further reduction. Both temperature and proton availability affect the rate of this isomerisation. Reduction of aliphatic nitrocompounds to the hydroxylamine is usually carried out in acid solution at 0-5° C to minimise oxime formation [14, 15], The hydroxylamine is stable towards further reduction in acid solution. Oximes in acid solution are reduced... 

Oximes, formation by nitrosation, 7, 6 Oxochromium(VI)-amine complexes, 53, 1 Oxo process, 56, 1... 

A new piperidine alkaloid Adalinine 352 was prepared in racemic form, using a rearrangement as a key step (equation 134). Enolate chemistry allowed double a-alkylation of cyclopentanone, producing 350 after oxime formation. Rearrangement provided a clear conversion into the lactam 351, easily converted to racemic Adalinine 352. 

The synthesis of the benzazepinone portion of benazepril began with monobromination of 1-tetralone (35), followed by oxime formation to give 36 (Scheme 10.9). A Beckmann rearrangement mediated by polyphosphoric acid provided the ring-expanded lactam 37. Displacement of the a-bromine with potassium phthalimide installed the necessary... 

A fast and straightforward approach to the large-scale production of fluorine-18-labelled peptides is based on the chemoselective oxime formation between an unprotected amino-oxy-functionalised peptide and 4-[ F]fluorobenzaldehyde (see Section 4.3.1.1). This reaction can be performed in aqueous media [275,276]. 

G. Henriksen, H. Kessler, M. Schwaiger, H.J. Wester, Chemoselective pre-conjugate radiohalogenation of unprotected mono- and multimeric peptides via oxime formation, Radiochim. Acta 92 (2004) 317-327. 

Further details of the photoaddition of N-nitrosopiperidine to a-pinene have been published.The claim of a-fenchen-6-one oxime formation (Vol. 7, p. 43) has been retracted the product is optically active carvone oxime. The stereochemistry and conformations of amino-oximes derived from a-pinene nitroso-chloride have been examined. ... 

A reference sample of (5)-3-piperidineethanol (18, see p 419) was prepared, starting from the known (/ )-3-oxocyclopentaneacetic acid (16) by (1) oxime formation to give 17, (2) Beckmann rearrangement, and (3) LiAlH4 reduction48. 

The free base is prepared by grinding the product with 25 gm of sodium bicarbonate with a small amount of water until a brown paste forms. This mixture is repeatedly extracted with ether. The ether extract is evaporated under reduced pressure. The crude base, which remains behind, is recrystallized from carbon tetrachloride, m.p. 144°-145°C dec. This product is presumed not to be quite pure because of the possibility of a-naphthaquinonimide oxime formation. 

Treatment of aliphatic active methylene compounds with such reagents normally leads to oxime formation. An exception is the nitrosation of compounds with active tertiary carbon atoms such as ethyl isopropyl ketone which are convertible into C-nitroso compounds. 

Furthermore, the possibility of the existence of dimeric nitroso compounds was not recognized until relatively recently. The characteristic light absorption attributed to the nitroso group is at about 700-750 mp. The possibility of dimerization or oxime formation or both reduces the molar extinction to a small value [30]. 

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