Phenacyl bromide oxidation

It appears that treatment of phenacyl bromides 1239 with methylhydrazine in refluxing acetic acid leads also to 1,4-disubstituted triazoles 1244. Fivefold excess of methylhydrazine is used in these reactions. According to the proposed mechanism, structures 1240-1243, methylhydrazine has a double role, as a condensing agent and an oxidant. In the final account, three molecules of methylhydrazine have to be used to produce one molecule of triazole 1244, two molecules of methylamine and one molecule of ammonia. The basic triazole 1244 (X = Y = H) is separated in 59% yield. The reactions go well with electron-donating substituents (for X = OH, the yield is 81%), but electron-withdrawing substituents can lower the yield dramatically (11% for X = N02) (Scheme 206) <2003JCM96>. 

Cromwell and Setter quiet38 2 re-examined earlier condensations of o-t)itrobenzaldehyde and phenacyl bromide, and likewise obtained a mixture of frww-o-nitrobcnzalaoetophenone oxide and its cw-isomer (Eq. 166). ... 

Narasaka and coworkers reported radical-polar crossover addition/cyclization reactions of phenacyl bromides 204 and electron-rich alkenes such as (silyl) enol ethers 205, catalyzed by the rhenium(I) complex 206 (Fig. 57) [302], The active catalyst 206A formed after thermal nitrogen elimination from 206 reduced 204 either directly or by oxidative addition/homolysis via rhenium enolate 204A to... 

There is one report of the use of /, yV-dialkylhydroxylamines to oxidize phenacyl bromides (equation 36). ... 

There is continumg interest in the organometalhc chemistry of Pd. This oxidation state has often been invoked as an intermediate in the reactions of Pd species with reactive acyl or alkyl halides. Spectroscopic evidence has been obtained for this hypothesis. When phenacyl bromide reacts with dimethylpalladium(n) complexes, such as PdMe2(bpy), a complex can be isolated at 0 °C, which is shown, by H NMR and X-ray crystallography, to be PdBrMe2(CH2COAr)(bpy) (equation 2). The same complex reacts with Mel to form PdIMe3(bpy). The d Pd complexes are expected to exhibit... 

Hydrogenolysis of 4-benzylpiperazine-2,6-diones over palladium-charcoal produced 4-unsubstituted piperazine-2,6-diones in high yield. The amino group in l-phenylpiperazine-2,6-dione underwent alkylation with benzyl chloride and phenacyl bromide, but not with simple alkyl halides (1638). Oxidative dimerizations of piperazine-2,6-diones in nitrobenzene have been studied (1639). 2,6-Bis(hydroxy-imino)piperazine heated with palladium-charcoal in o-dichlorobenzene gave 2,6-diaminopyrazine (465). 

The oxidants dimethyl sulfoxide and nitroso compounds react easily with oL-bromo ketones and convert them into a-dicarbonyl compounds. The reaction with nitroso compounds is usually carried out in the presence of pyridine and proceeds through a nitrone stage. Phenacyl bromide (a-bromoacetophenone) is thus transformed first into phenacylpyridinium bromide and further, with nitrosobenzene, into a-ketoaldonitrone, which is subsequently treated with hydroxylamine to give phenylglyoxal monoxime or with phenylhydrazine to give phenylglyoxal osazone [985] (equation 411). 

Reaction of quinazoline with phenacyl bromides and subsequently with dimethyl acetylenedicarboxylate or ethyl propiolate in propylene oxide at ambient temperature gave the pyrrolo[l,2-c]quinazolines 47. The latter are formed in a [3 + 2] dipolar cycloaddition between the quinazolinium ylides 46, generated in situ, and the acetylene derivatives. 

Oxidation. Komblum found that phenacyl bromide, as well as its p-halo, p-nitro, and p-phenyl derivatives, can be oxidized to glyoxals by dissolving it in... 

Photolysis of ring-substituted phenacyl bromides gives ketyl radicals which in the presence of alcohols leads to the corresponding carbonyl compounds.Two different chain mechanisms seem to operate and in the presence of methanol, oxidation predominantly occurs by hydrogen transfer whereas in the presence of isopropanol, acetone is formed mainly by an electron transfer process. 

The most useful procedure utilises a 1,4-keto-ester giving a dihydro-pyridazinone, which can be easily dehydrogenated to the fully aromatic heterocycle, often by C-bromination then dehydrobromination alternatively, simple air oxidation can often suffice. 6-Aryl-pyridazin-3-ones have been produced by this route in a number of ways using an a-amino nitrile as a masked ketone in the four-carbon component, or by reaction of an acetophenone with glyoxylic acid and then hydrazine. Friedel-Crafts acylation using succinic anhydride is an alternative route to 1,4-keto-acids, reaction with hydrazine giving 6-aryl-pyridazinones. Alkylation of an enamine with a phenacyl bromide prodnces 1-aryl-l,4-diketones, allowing synthesis of 3-aryl-pyridazines. ... 

ZOR1097>. When the zinc selenide (170) is reacted with phenacyl bromide 3-phenyl-2//-l,4-benzoselenazine (173) is produced (Scheme 41). This compound is unstable and undergoes oxidative dimerization [Pg.1011]

The N-oxides 27 were obtained directly by boiling solutions of the oximes 26 with either bromoacetaldehyde or bromoacetone in acetonitrile containing 48% hydrobromic acid. Phenacyl bromide in acetonitrile provided the quaternized intermediates 28, which were cyclized to the corresponding 6-phenyl-7-oxides (29) by treatment with concentrated sulfuric acid. 

Quaternization of the oximes 23 with a-bromoketones 24 provides a useful route to the 2-oxides 25 of the ring system. Treatment of the aldoxime 23 (R = H) with phenacyl bromide yields the intermediate quaternary salt 26, which may be cyclized with hydrobromic acid. Similarly 3-unsubstituted compounds are available from haloacetaldehyde derivatives. Thus bromoacetaldehyde in refluxing acetonitrile converts the oxime 23 (R = Et) into the dihydro compound 27, which on boiling in hydrobromic acid provides the aromatic compound 28. Sequential treatment of the aldoxime 23 (R = H) with chloroacetaldehyde oxime and concentrated hydrobromic acid yields the iV-oxide 29 of pyrido[l,2-ajpyrazinium bromide without isolation of the intermediate quaternary salt. ... 

Reaction of 46 with ethylene oxide followed by phosphoryl chloride treatment of the resultant bis(hydroxyethyl)amine afforded the chloroethyl compound 47. Heating the chloroacetyl derivative 48 of the amine results in cyclization to the oxo derivative 49, and refluxing the amine in ethanol with phenacyl bromide provides the phenyl compound 50. ... 

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