Oximes, dimethyl carbonate

The reaction of ketoximes 235 with dimethyl carbonate in the presence of K2CO3, carried out in an autoclave at 180-190 °C, afforded 3-methyl-4,5-disubstituted 4-oxazolin-2-ones 236 (equation 102). The formation of compounds 236 occurred via [3,3]sigma-tropic rearrangement of intermediates of the oxime methylated with dimethyl carbonate. 

The methoxide-catalysed methanolysis of the substituted benzamide (7-(phenoxycar-bonyl) oxime (83) proceeds in two steps in the first step, the phenoxy group is substituted by a methoxy group to yield (84), and in the second step, benzamide oximate (85) is eliminated and dimethyl carbonate (86) forms (Scheme 15). ... 

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. ... 

Addition of anionic nucleophiles to alkenes and to heteronuclear double bond systems (C=0, C=S) also lies within the scope of this Section. Chloride and cyanide ions are effieient initiators of the polymerization and copolymerization of acrylonitrile in dipolar non-HBD solvents, as reported by Parker [6], Even some 1,3-dipolar cycloaddition reactions leading to heterocyclic compounds are often better carried out in dipolar non-HBD solvents in order to increase rates and yields [311], The rate of alkaline hydrolysis of ethyl and 4-nitrophenyl acetate in dimethyl sulfoxide/water mixtures increases with increasing dimethyl sulfoxide concentration due to the increased activity of the hydroxide ion. This is presumably caused by its reduced solvation in the dipolar non-HBD solvent [312, 313]. Dimethyl sulfoxide greatly accelerates the formation of oximes from carbonyl compounds and hydroxylamine, as shown for substituted 9-oxofluorenes [314]. Nucleophilic attack on carbon disulfide by cyanide ion is possible only in A,A-dimethylformamide [315]. The fluoride ion, dissolved as tetraalkylammo-nium fluoride in dipolar difluoromethane, even reacts with carbon dioxide to yield the fluorocarbonate ion, F-C02 [840]. 

During catalytic hydrogenation of nitro derivatives, partial reduction of the nitro group yields azo, hydrazo, hydroxylamine, nitroso, or oxime functions, in side products, as a result of catalyst deactivation. Partial reduction may become synthetically useful under carefully chosen conditions, and in substrates where the new formed function cannot interact within the molecule. Nitrobenzene hydrogenation over platinum-on-carbon in a mixture alcohol-dimethyl sulfoxide (as promoter) produces high yields of phenylhydroxylamines ... 

Another application of the Hantzsch method is in the synthesis of the aminothiazole coupling partner in the synthesis of the antibiotic cefdinir. The reactive methylene carbon of ethyl acetoacetate is first functionalized to the oxime after which a-chlorination is brought about to furnish the chloro-oxime substrate for Hantzsch synthesis with thiourea. A,jV-Dimethyl aniline is used as a base in the thiazole formation. ... 

Oximes as well as amides (p. 249) are converted into nitriles by some silicon derivatives. Hexamethylcyclotrisilazane (8) when heated at 210° for 6 hr with benzaldoxime gives benzonitrile in 72% yield [35]. Carbodiimides in pyridine have a similar action on amides [48]. By replacing pyridine by triethylamine and either ether or carbon tetrachloride, and addition of acetyl or phenacetyl chloride, aldoximes may be converted to nitriles at low temperature [62] examples are PhCN (86.6%), PhCH = CH.CN, (81.4%) and 2-cyanofuran (82.6%). A car-bodi-imide, trifluoroacetic acid and dimethyl sulphoxide (DMSO) mixture has been shown to dehydrate 4-bromobenzaldoxime [63]. 

Saxena et al. studied the adsorption of dimethyl methyl phosphonate (DMMP) as a stimulant for Sarin, which is a highly toxic warfare gas agent. The adsorption was carried out on an activated carbon, a whetlerite and activated carbon impregnated with copper hexafluorocacetylacetonate (1) copper trifluoro acetyl-acetonate and a copper oxime. The adsorption isotherms are Type 1 of the BET classification and show maximum adsorption in the case of activated carbon (1). The amount adsorbed was 68.5 weight percent on (1). The adsorption involved both physisorption and chemisorption. TGA and IR studies of DMMP loaded activated carbons, and mass spectric analysis of the decomposition products showed that the decomposition products were methyl methyl phosponic acid and methylphosphonic acid. 

Dimethyl-cyclopentanon-(4)-carbon< B5iire.(2)-ozmi 10, 611. l.l-Dimetliyl-oyolopentanon-(6)-carbon Baore.(2)-oxim 10, 611. /-Umpropyl-batyrolacton-y-earboiu ure-amid 18 383. 

Dimethyl-oyabhexen-(3)-on-(6)-carbon> 8aiire-(2)-athyle8ter-oxim 10, 634. 

Cobalt(II)-bis((Z)-2-hydroxy-5,5-dimethyl-1 -(4-methylpiperazin-l -yl)hex-2-ene-1,4-dione) efficiently catalyses the aerobic oxidative 5-exo cyclization of )5,) -unsaturated oximes to give isoxazolines. Carbon-centred radicals are generated in the basic cyclization step. The predominant oxidative products of the reaction carried out in the presence of i-PrOH and TBHP are (16), whereas reductive products (17) are selectively obtained when the reaction is carried out in toluene in the presence of cyclohexa-1, 4-diene. " ... 

Radical cyclization continues to be one of the most popular radical reaction classes used in synthesis. By far the majority of published cyclization reactions are 5-exo in nature and this year is no exception. The rates of 5-exo cyclization reactions continue to be measured. For example, the rate constants for the 5-exo cyclizations of the 6,6-diphenylhex-5-enyl, 1-methyl-6,6-diphenylhex-5-enyl and the 1,1-dimethyl-6,6-diphenylhex-5-enyl radicals have been measured by laser flash photolysis studies and Arrhenius parameters determined. The relative rate constants for cyclization, and the reaction with PhSeH, were determined at 20 °C. At 20 °C the rates of the three primary, secondary and tertiary radicals with PhSeH were approximately (1.2 0.1) X 10 lmol s The rate constants for alkyl radicals calibrated by competition reactions with PhSeH and PhSH were found to be 30-40% smaller than previously reported and thus it was concluded that derived rate constants for some fast radical reactions may have to be adjusted accordingly. The rate constants for the 5-exo cyclization of secondary radicals on to hydrazones and oxime ethers have been determined. The fastest rate constants were observed for the IV-benzoylhydrazone acceptor. The rate constants were found to be approximately 800 times faster than for the corresponding 5-exo cyclization on to alkenes." Other work has measured the rate constants of cyclization of a range of fluorinated hex-5-enyl, hept-6-enyl, oct-7-enyl and non-8-enyl radicals. Not only were the rate constants measured but the regioselectivity of cyclization was compared with that for the aU-carbon homologues." The 6-exo cyclization of 1,1,2,2-tetrafluoro- and l,l,2,2,3,3,4,4-octafluorohept-6-enyl radicals were found to be approximately 10 times faster than those for the parent... 

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