Cyclohexane reactions with nucleophiles

CycJohexyl free radicals, generated by photolysis of t-butyl peroxide in excess cyclohexane, also possess nucleophilic character (410). Their attack on thiazole in neutral medium leads to an increase of the 2-isomer and a decrease of 5-isomer relative to the phenylation reaction, in agreement with the positive charge of the 2-position and the negative charge of the 5-position (6). 

The photo-induced electron transfer of l,4-bis(methylene)cyclohexane in acetonitrile-methanol solution with 1,4-dicyanobenzene (DCB) affords two products, both consistent with nucleophilic attack on the radical cation followed by reduction and protonation or by combination with DCB ).63 In the absence of a nucleophile, the product mixture is highly complex, as is the case under electro-oxidative conditions. Under UV irradiation, /nmv-stilbene undergoes dimerization and oxygenation (to benzaldehyde) by a single-electron mechanism in the presence of a sensitizer such as 2,4,6-triphenylpyrilium tetrafluoroborate (TPT).64 This reaction was found to yield a similar product mixture with the sulfur analogue of TPT and their relative merits as well as electrochemical and photophysical properties are discussed. 

The nucleophilicity of chloride ion in the SN2 reaction with methyl benzenesulfonate was found to decrease as the solvent was changed from cyclohexane to acetone to butan-2-one to DMF to acetonitrile to methanol.78 Activation parameters in each solvent are reported. 

Nucleophilic photosubstitution reactions of benzylic chlorides have also been observed to occur with nucleophiles other than the alcohol solvents. n-Nucleophiles such as amine solvents147 and halide ions and acetate ions148, as well as 7r-nucleophiles such as toluene149 have been used. The latter, a photoalkylation reaction, was achieved by irradiation of benzyl chloride absorbed within zeolite micropores in a slurry in cyclohexane. In cyclohexane itself only products of PhCH2 are formed. This large medium effect is due to the strong electrostatic fields experienced in the zeolite cavities149. 

The lithium salt of diethyl 2-propenylphosphonate behaves as an ambident nucleophile in reactions with a variety of electrophilic reagents. In reaction with methyl methacrylate, the intermediate formed in the lirsl step (conjugate addition at the y-carbon of the phosphonate) has a carbanionic center developed at C-5. The second step involves intermolecular conjugate addition to a second molecule of methyl methacrylate, yielding an intermediate capable of the final 1,6-cyclization to produce a phosphonylated polyfunctionalized derivative of cyclohexane in good overall yield (60%, Scheme 8.63). ... 

This equation is in good agreement with experimental results. An analysis of this dependence results in the following ratio of constants k -.k2. k-i = 100 14 0.6 (for cyclohexane at 100 °C), i.e in effect, the uncharged complex S2PtCl2 is the most active. This may be an indication of the importance of the electrophilic properties of the platinum complex in the reaction with hydrocarbons, although an appreciable value of the rate constant of such a moiety as PtCl, in its reaction with alkanes in aqueous solution, does not fit the usual concepts of electrophiles very well. It has been shown that the particular Pt(II) complexes obtained, which should form positive ions upon solution in water, PtCI(H20)j and [Pt(H20)4] react more slowly with alkanes than PtCl2. This demonstrates a more complicated nature of interaction of the bivalent platinum and the hydrocarbon molecule than that of the interaction of an electrophile with a nucleophile. 

For another classical problem of nucleophilic aliphatic substitution and rearrangement, namely pinacolic deaminations and rearrangements, the use of cyclohexane derivatives with a tert-hvXyX group instead of open-chain alkane derivatives was very helpful. The stereochemistry of these reactions was studied first by Bernstein and Whitmore (1939). Specific labeling with used first by Collins and his coworkers (Benjamin et al., 1957), helped significantly to elucidate the complex pathway of pinacolic deamination. Even summarizing the results would take far too much space here. 

The reaction with cyclohexane 337 Electrophilic reactions 338 Nucleophilic reations 339 Addition reactions 340 Thermal oligomerization 342 Rearrangements 345 Perchlorinated nitrogen compounds 345 Perchlorination of amines 345... 

Another extensive study involves the displacement of THF from [Go(GO)L(NO)(THF)] [L = CO, PPh3, and P(OPh)3] generated by flash photolysis of [Co(CO)2L(NO)] in THF. Reactions with various nucleophiles, L, were strictly first order in [L ]. Reactions in mixed THF-cyclohexane solvents with... 

The alkaline fading of crystal violet (4-Me2NC6H4)3C+ in cationic W/O microemulsions of CTABr-alcohol-cyclohexane occurs in the water pools [113]. The corresponding reactions of crystal violet and malachite green, (4-Me2NC6H4)2C Ph, in anionic W/O AOT-isooctane microemulsions also occur in the water pools, and rate data were analyzed in terms of their size and the competing base-promoted hydrolysis of AOT [114]. This reaction with crystal violet is strongly inhibited by ClOj, which pairs with the carbocation and blocks nucleophilic attack,... 

A newer possibility for the intramolecular cyclization of the phosphorane/ylide was demonstrated by the final outcome of the reaction of TPP, DAAD and cyclohexane-l,3-diones after microwave irradiation of the intermediate. Electron-poor 2H-chromenes were the products of the reactions (Scheme 111). Interestingly, hydroquinone acted as a C-nucleophile in reaction with the TPP-DAAD adduct to result in the formation of a 3-aryl phosphorane that provided another 2H-chromene derivative on K2HPO4 catalyzed intramolecular ring closure (Scheme 112). ... 

The photo-NOCAS reaction with 2,6-dimethyl-l,6-heptadiene gave two major cyclic aryl-methoxy adducts (a cyclohexane and a cycloheptane) as well as an acyclic heptene adduct Variation in concentration of the nucleophile, methanol, and co-donor, biphenyl, has been shown to affect the product ratios. Further applications of the photo-NOCAS S 2Ar reactions with the aUeyl-4-enols, a-terpineol, limonene, 2-methyl-2-butene, 2,3-dimethyl-2-butene, (3-myrcene, and 1,4-bis (methylene) cyclohexene have been reported.The aryl-methoxy adduct product ratios have been investigated and discussed in terms of the stability of radical intermediates and the factors controlling the regiochemistry of reaction with the nucleophiles alcohols, cyanide, and fluoride attempts to justify the results by ab initio molecular orbital calculations have been made. The photo-NOCAS reaction with 2-methylpropene in the absence of methanol and a donor molecule has shown that solvent acetonitrile can act as a nucleophile. Under these conditions a tetrahydroisoquinoline product is formed, prior to HCN elimination, in high yield as illustrated in Scheme 8. The adduct product formation was rationalized on the basis of the relatively high oxidation potential of the olefin. 

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