Dibromides reduction

Coche, L., Deronzier, A., and Moutet, J. C., An attempt al the preparative alkyl dibromide reduction using electrodes coated by a polypyrrole film containing the viologen (4,4 -bipyridinium) system, J. Electroanal. Chem., 198, 187-193 (1986). Grimshaw, J., and Perera, S. D., Redox behaviour of a polypyrrole modified electrode where the pyrrole has N-substituted 9-cyanoanthracene groups, J. Electroanal. Chem., 265, 335-339 (1989). 

Polymer-modified electrodes were used for alkyl dibromide reduction (Eq. 14)) 86-88)... 

Trimethylene dibromide (Section 111,35) is easily prepared from commercial trimethj lene glycol, whilst hexamethylene dibromide (1 O dibromohexane) is obtained by the red P - Br reaction upon the glycol 1 6-hexanediol is prepared by the reduction of diethyl adipate (sodium and alcohol lithium aluminium hydride or copper-chromium oxide and hydrogen under pressure). Penta-methylene dibromide (1 5-dibromopentane) is readily produced by the red P-Brj method from the commercially available 1 5 pentanediol or tetra-hydropyran (Section 111,37). Pentamethylene dibromide is also formed by the action of phosphorus pentabromide upon benzoyl piperidine (I) (from benzoyl chloride and piperidine) ... 

Tungsten dibromide [13470-10-5] WBr2, formed by the partial reduction of the pentabromide with hydrogen, is a black powder that decomposes at... 

There are several laboratory methods useful for the preparation of suberic acid. One starting material is 1,6-hexanediol which can be converted to the dibromide with HBr. Reaction of the dibromide with NaCN gives the dinitrile which can be hydrolyzed to suberic acid. The overall yield is 76% (42). Another laboratory method is the condensation of 1,3-cyclohexanedione with ethyl bromoacetate foUowed by reductive cleavage to give suberic acid in 50% yield (43). 

Ceroplastol synthesis, 1, 428 Cetyl alcohol synthesis, 1, 478 Chaetoglobasins structures, 4, 376 Chalcone, o -azido-2 -oxy-synthesis, 3, 823 Chalcone, 2-hydroxy-reduction, 3, 751 Chalcone, 2 -hydroxy-mass spectra, 3, 618 Chalcone dibromides flavone synthesis from, 3, 823 Chalcones polymers, 1, 304 Chanoclavine synthesis, 6, 423 Charge density waves in stacks of ions, 1, 351-352 Chartreusin... 

Toluene is a useful co-solvent in metal-ammonia reductions as first reported by Chapman and his colleagues. The author has found that a toluene-tetrahydrofuran-ammonia mixture (1 1 2) is a particularly useful medium for various metal-ammonia reductions. Procedure 8a (section V) describes the reduction of 17-ethyl-19-nortestosterone in such a system. Ethylene dibromide is used to quench excess lithium. Trituration of the total crude reduction product with methanol affords an 85% yield of 4,5a-dihydro-17-ethyl-19-nortestosterone, mp 207-213° (after sintering at 198°), reported mp 212-213°. For the same reduction using Procedure 5 (section V), Bowers et al obtained a 60% yield of crude product, mp, 196-199°, after column chromatography of the total reduction product. A similar reduction of 17-ethynyl-19-nortestosterone is described in Procedure 8b (section V). The steroid concentration in the toluene-tetrahydrofuran-ammonia system is 0.05 M whereas in the ether-dioxane-ammonia system it is 0.029 M. 

The stereochemistry of the dibromides does not appear to affect the usefulness for regenerating olefins with zinc or chromous ion however, significant differences in ease of reduction have been observed. Thus, the diequatorial 3j5,4a-dibromocholestane (121) is 1 % reacted under conditions which give a 91 % conversion of the diaxial 3a,4j5-isomer (122). 

Dibenzo[d,g][l,5]telluroazocines 65 are the only representatives of Te, N-containing eight-membered heterocycles known thus far. Treatment of bis(2-bromomethylphenyl)tellurium dibromide 66 with methylamine followed by reduction of the reaction mixture with sodium sulfide gives, instead of the expected... 

R R M were prepared by reduction of the dibromides R R MBr2 with lithium naphthalenide (method A), by thermolysis of a disilene (method B), and the ligand exchange of divalent group 14 element species (method C). In all cases except for the synthesis of Tip2PbS4, exclusively tetrasulfides R R MS4... 

Two-electron reduction of 4,4 -(l,3-propanediyl)bis-(iV-methylpyridinium) dibromide with sodium amalgam affords bis-l,4-dihydropyridine 46 <96CL151>. 

The reduction ofsec-, and /-butyl bromide, of tnins-1,2-dibromocyclohexane and other vicinal dibromides by low oxidation state iron porphyrins has been used as a mechanistic probe for investigating specific details of electron transfer I .v. 5n2 mechanisms, redox catalysis v.v chemical catalysis and inner sphere v.v outer sphere electron transfer processes7 The reaction of reduced iron porphyrins with alkyl-containing supporting electrolytes used in electrochemistry has also been observed, in which the electrolyte (tetraalkyl ammonium ions) can act as the source of the R group in electrogenerated Fe(Por)R. ... 

The stereospeciflcity of dehalogenation of vicinal dibromides to olefins was examined for reducing agents including Cr(II), iodide, and Fe° (Totten et al. 2001). For dibromostilbene, the ( )-stilbene represented >70% of the total olefin that was produced, and for threo-dibromopentane reduction by Cr(Il) produced ca. 70% of ( )-pent-2-ene, whereas values for iodide and Fe° were <5% of this. 

As vicinal dibromides are usually made by bromination of alkenes, their utility for synthesis is limited, except for temporary masking of a double bond. Much more frequently it is desirable to convert a diol to an alkene, and several useful procedures have been developed. The reductive deoxygenation of diols via thiono carbonates was... 

The first synthesis of thiepin 1,1-dioxide (131) was performed by Mock in 1967 75>. With exess bromine in chloroform 2,7-dihydrothiepin 1,1-dioxide (129), prepared by 1,6-addition of sulfur dioxide to m-hexatriene, gave a dibromide 130 which, on treatment with two equivalents of triethylamine, afforded 131. Upon catalytic reduction, 131 rapidly absorbed three molar equivalents of hydrogen to yield hexahydrothiepin 1,1-dioxide (132). The 1,1-dioxide 131 is a fairly stable compound ... 

The electrochemical reduction of 1,3-dibromides to cyclopropanes (30 31) appears to be fairly general 4J 44> an(j has been applied to the synthesis of some rather strained ring systems, e.g., 32, 33, and 34. Rifi has sug-... 

To test this point, McKeon and Koch examined the preparative scale electrochemical reduction of the diaxial bromides 43 and 46 in aqueous DMF 49>. They found only the corresponding olefins as products, under analytical conditions which could have detected as little as 3% of the alkanes, had they been formed. It is unfortunate that a dibromide for which = 90° was not investigated by these workers. Reduction of such a compound ought to be stepwise, and alkane could be formed, especially in a proton-donating medium. Finally, Nelson and coworkers have suggested from their study of a series of rigid vi-... 

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

Chemiluminescence also occurs during electrolysis of mixtures of DPACI2 99 and rubrene or perylene In the case of rubrene the chemiluminescence matches the fluorescence of the latter at the reduction potential of rubrene radical anion formation ( — 1.4 V) at —1.9 V, the reduction potential of DPA radical anion, a mixed emission is observed consisting of rubrene and DPA fluorescence. Similar results were obtained with the dibromide 100 and DPA and/or rubrene. An energy-transfer mechanism from excited DPA to rubrene could not be detected under the reaction conditions (see also 154>). There seems to be no explanation yet as to why, in mixtures of halides like DPACI2 and aromatic hydrocarbons, electrogenerated chemiluminescence always stems from that hydrocarbon which is most easily reduced. A great number of aryl and alkyl halides is reported to exhibit this type of rather efficient chemiluminescence 155>. 

The bromo-aryl groups are first linked by (5,5 )-stilbene diol to form the dibromide 33. Compound 33 is then dilithiated with t-BuLi at —78°C, followed by addition of CuCN. Intermediate 34 is presumably formed during the reaction. Reductive elimination promoted by molecular oxygen provides compound 35 at 77% yield with 93 7 diasteroselectivity. The final biaryl compound ellagi-... 

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