Pyridine 1-oxides mercuriation

C2oH2oCl2Hg2NnOi2r Pyridine 1-oxide mercury(l) perchlorate dimer, 39B, 770... 

C3oH3oCl2HgN60ift, Hexakis(pyridine 1-oxide)mercury(II) bisperchlor-ate, 39B, 773... 

C5H5Cdl2NO, (Pyridine-N-oxide)cadmium diiodide, 40B, 934 C5H5Cl2HgNO, (Pyridine-N-oxide)mercury dichloride, 40B, 934 CgHgCuOg, Copper croconate, 29, 669... 

Electrophilic mercuration of isoxazoles parallels that of pyridine and other azole derivatives. The reaction of 3,5-disubstituted isoxazoles with raercury(II) acetate results in a very high yield of 4-acetoxymercury derivatives which can be converted into 4-broraoisoxazoles. Thus, the reaction of 5-phenylisoxazole (64) with mercury(II) acetate gave mercuriacetate (88) (in 90% yield), which after treatment with potassium bromide and bromine gave 4-bromo-5-phenylisoxazole (89) in 65% yield. The unsubstituted isoxazole, however, is oxidized under the same reaction conditions, giving mercury(I) salts. 

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

Indium Iodine Acetonitrile, nitrogen dioxide, mercury(II) bromide, sulfur Acetaldehyde, acetylene, aluminum, ammonia (aqueous or anhydrous), antimony, bromine pentafluoride, carbides, cesium oxide, chlorine, ethanol, fluorine, formamide, lithium, magnesium, phosphorus, pyridine, silver azide, sulfur trioxide... 

Reactions of methoxycarbonylformonitrile, furonitrile and substituted benzoni-trile oxides (4-Me, 4-OMe, 3-OMe, 4-C1, 3-C1, 2,4-di-Cl, 4-F as substituents) with dimethyl 7-(diphenylmethylene)bicyclo[2.2. l]hept-2-ene-5,6-dicarboxylate led exclusively to exo cycloadducts 82 (R = C02Me, 2-furyl, substituted phenyl), which, on irradiation with a low-pressure mercury lamp, afforded 3-azabicyclo [4.3.0]nonadiene-7,8-dicarboxylates 83 as the only products. The 1,3-dipolar cycloaddition, followed by a photorearrangement, provides a new method for obtaining tetrahydro-27/ -pyridine derivatives from cyclopentadiene (245). 

Other reagents that convert benzylic halides to aldehydes are 2-nitropropane-NaOEt in EtOH,336 mercury(I) nitrate followed by ethanolic alkali,337 and pyridine followed by p-nitrosodimethylaniline and then water. The last procedure is called the Krohnke reaction. Primary halides in general have been oxidized to aldehydes by trimethylamine oxide,338 by... 

Treatment 2,3-dichloro-5-(trichloromethyl)pyridine in anhydrous hydrogen fluoride with mercury(II) oxide (red) at room temperature for 22 hours provides 2,3-dichloro-5-(tri-fluoromethyl)pyridine in 98% yield.59... 

Like benzenoid hydrocarbons, pyridine-like heterocycles give well-developed two-electron waves on reduction at the dropping mercury electrode. The latter are polarographically much more reducible than the former. This can be explained easily in terms of the HMO theory It is assumed (cf. ref. 3) that the value of the half-wave potential is determined essentially by the energy of the lowest free 7r-molecular orbital (LFMO) of the compound to be reduced, and for models of hetero analogues this quantity is always lower than that for the parent hydrocarbons. Introduction of an additional heteroatom into the molecule leads to a further enhancement of the ease of polarographic reducibility.95 On the other hand, anodic oxidation of the heterocyclic compounds is so much more difficult in comparison with benzenoid hydrocarbons that they are not oxidizable under the usual polarographic conditions. An explanation in terms of the HMO theory is obvious. 

Isoquinoline forms a 4-acetoxymercuri derivative. Pyridine 1-oxide is mercurated predominantly in the 2-position, but increasing acidity increases the proportion of 3-mercuri product formed. 

Mercury(II) chloride, 175, 182 Mercury(II) trifluoroacetate, 175 Molybdenum Compounds Molybdenum carbonyl, 194 Molybdenum(VI) oxide, 279 Oxodiperoxymolybdenum(pyridine)-(hexamethylphosphoric triamide),... 

An early procedure used triethyl phosphate directly on the diketone, but better yields are obtained by the oxidation of the corresponding dihydrazone 42 The oxidant may be mercury(n) oxide, which is rather expensive 43 alternatively copper(i) chloride in dichloromethane and pyridine is oxidised with oxygen gas, and the derived complex is then used to oxidise the dihydrazone to the acetylenic group with the evolution of nitrogen.44 The reaction is illustrated by the conversion of benzil dihydrazone into diphenylacetylene (Expt 5.25). 

A mixture of 74 parts of ethyl 4-[[[2-[(2-furanylmethyl)amino]-3-pyridinyl]aminothioxomethyl]amino]-l-piperidinecarboxylate, 96 parts of mercury (II) oxide, 0.1 parts of sulfur and 800 parts of ethanol was stirred and refluxed for 3 h. The reaction mixture was filtered over Hyflo and the filtrate was evaporated to give 52.5 parts (79%) of ethyl 4-[[3-(2-furanylmethyl)-3H-imidazo[4,5-b]pyridin-2-yl]amino]-l-piperidinecarboxylate melting point 149.2°C (crystallized from acetonitrile). 

Conditions for reducing pyridine N-oxides to pyridines have been worked out1S4>. In general, this reaction proceeds with good yields in 20 % aqueous sulfuric acid under constant current conditions at mercury or lead electrodes, provided there is no easily reducible group present in the molecule (e.g., the nitro group). 

The preparation and crystal structure determination of mercury(i) complexes of composition Hg2L2X2, Hg2L4X2, and Hg2L6X2 have been described,178-180 where L = 3-chloropyridine, pyridine N-oxide, and triphenylphosphine oxide, respectively. 

Cyclization of enone (9) in hexane with boron trifluorideetherate in presence of 1,2-ethanedithiol, followed by hydrolysis with mercury (II) chloride in acetonitrile, yielded the cis-isomer (10) (16%) and transisomer (11) (28%). Reduction of (10) with lithium aluminium hydride in tetrahydrofuran followed by acetylation with acetic anhydride and pyridine gave two epimeric acetates (12) (32%) and (13) (52%) whose configuration was determined by NMR spectroscopy. Oxidation of (12) with Jones reagent afforded ketone (14) which was converted to the a, 3-unsaturated ketone (15) by bromination with pyridinium tribromide in dichloromethane followed by dehydrobromination with lithium carbonate and lithium bromide in dimethylformamide. Ketone (15), on catalytic hydrogenation with Pd-C in the presence of perchloric acid, produced compound (16) (72%) and (14) (17%). The compound (16) was converted to alcohol (17) by reduction with lithium aluminium hydride. 

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