Cyclohexene equivalent hydrogens

Catalytic hydrogenation of benzene under pressure by using Raney Ni as a catalyst results in the addition of three molar equivalents of hydrogen. First, benzene is converted into cyclohexadiene, which is reduced to cyclohexene. The hydrogenation of cyclohexadiene and cyclohexene is faster than the hydrogenation of benzene (aromatic compound). Similarly, catalytic hydrogenation of naphthalene in the presence of a Ni catalyst gives tetralin and then decalin. 

When an alkene reacts with BH3 in THF solution, rapid addition to the double bond occurs three times and a tricilkylborcme, R3B, is formed. For example, 1 molar equivalent of BH3 adds to 3 molar equivalents of cyclohexene to yield tricyclohexylborane. When tricvclohexylborane is then treated with aqueous hydrogen peroxide (H2C>2) in basic solution, an oxidation takes place. The three C-B bonds are broken, -OH groups bond to the three carbons, and 3 equivalents of cyclohexanol are produced. The net effect of the... 

The epoxidation method developed by Noyori was subsequently applied to the direct formation of dicarboxylic acids from olefins [55], Cyclohexene was oxidized to adipic acid in 93% yield with the tungstate/ammonium bisulfate system and 4 equivalents of hydrogen peroxide. The selectivity problem associated with the Noyori method was circumvented to a certain degree by the improvements introduced by Jacobs and coworkers [56]. Additional amounts of (aminomethyl)phos-phonic acid and Na2W04 were introduced into the standard catalytic mixture, and the pH of the reaction media was adjusted to 4.2-5 with aqueous NaOH. These changes allowed for the formation of epoxides from ot-pinene, 1 -phenyl- 1-cyclohex-ene, and indene, with high levels of conversion and good selectivity (Scheme 6.3). 

If cyclohexanecarboxaldehyde is incubated with CYP2B4, NADPH, and cytochrome P450 reductase, the aldehyde-cyclohexyl ring carbon-carbon bond is cleaved generating cyclohexene and formic acid (150) (Fig. 4.81). The reaction is supported if hydrogen peroxide replaces NADPH and cytochrome P450 reductase but is not supported if other oxidants at the same oxidation equivalent as peroxide but bypass the peroxy form of P450 such as iodosobenzene, m-chloroperbenzoic acid, or cumyl hydroperoxide are used. These... 

The hydrofluorination of alkenes with anhydrous hydrogen fluoride has been already described extensively in Houben-Weyl, Vol. 5/3, pp 100-101. In the case of ethene, the yield of fluoroethane increases on raising the temperature (90°C, 20-25 atm), however, the procedure should be carried out at lower temperatures with higher alkenes because of their tendency to polymerize thus, 2-fluoropropane is formed in 60-75% yield at 0-45 C. Similar procedures have been described for 2-fluorobutane, 2-fluoro-2-methylpropane and 2-fluoro-2-methyl-butane from but-l-ene, 2-methylpropene and 2-methylbut-2-ene, respectively.63 Cyclohexene reacts at — 78 C with hydrogen fluoride to give fluorocyclohexane (70%) at 100 C polymerization is observed.59,60 Two equivalents of hydrogen fluoride to allene are taken up at — 70 C, to form 2,2-difluoropropane (50%).64... 

Previous work has shown that the electronic characteristics of the benzene substituent in triarylphosphine chlororhodium complexes have a marked influence on the rate of olefin hydrogenation catalyzed by these compounds. Thus, in the hydrogenation of cyclohexene using L3RhCl the rate decreased as L = tri-p-methoxyphenylphosphine > triphenylphosphine > tri-p-fluorophenylphosphine (14). In the hydrogenation of 1-hexene with catalysts prepared by treating dicyclooctene rhodium chloride with 2.2-2.5 equivalents of substituted triarylphosphines, the substituent effect on the rate was p-methoxy > p-methyl >> p-chloro (15). No mention could be found of any product stereochemistry studies using this type of catalyst. 

Cyclohexen-l-yl isocyanide 1 known as Armstrong convertible isocyanide has also been called universal isocyanide . It was prepared in 1963 by Ugi and Rose-ndahl [5] to be used as a synthetic equivalent of the unknown hydrogen isocyanide . The Ugi-4CR between 1, cyclohexanone N-benzylimine 2, and formic acid afforded N-cyclohexen-l-yl amide 3, which was cleaved in acidic medium to afford the primary a-acylamino amide 4 rather than the N-substituted amides usually obtained by the Ugi-4CR (Scheme 2.1). 

Scheme 2.1. 1-Cyclohexen-1-yl isocyanide as a synthetic equivalent of hydrogen isocyanide.

After debenzylation (Pd-C, cyclohexene) of the hypercores (e.g., 25) by transfer hydrogenation, they were treated with aryl branched, benzyl ether dendrons (Scheme 5.6) that were prepared by similar iterative transformations,1271 i.e., benzylic bromination and phenolic O-alkylation (See Section 5.4.2). Thus, hexaphenol core 27 was reacted with six equivalents of the benzylic bromide building block 28 to give the benzyloxy terminated dendrimer 29. Key features of these dendrimers include cores with flexible alkyl spacers and a three-directional, quaternary carbon branching center. 

The epoxide method can be used with epoxides of acyclic [ 165-168] and cyclic [169-172] alkenes with a visible bias for cyclohexene oxide as the epoxide of choice. The epoxide is usually reacted with unsubstituted imidazole creating a neutral molecule. If the epoxide is reacted with an N-substituted imidazole, a zwitterionic molecule is created as the hydroxide functional group in the sidearm lacks the imidazole NH hydrogen atom to be proto-nated. In this case, addition of one equivalent of acid provides protonation to the alcohol and the counteranion for the formation of the imidazolium salt. 

Nitroalkenes can also be regarded as dienophilic alkene equivalents owing to the recently reported substitution of the nitro group by a hydrogen atom. Thus treatment of the cycloadducts with BusSnH in the presence of AIBN opens a new regioselective (but stereo-random) access to cyclohexenes (Scheme 11). 0... 

Research in the laboratory of H.M.I. Osborn showed that the use of cyclohexene derivatives as nucleophiles in the Lewis acid-mediated Type I carbon-Ferrier reaction of 3-0-acetylated glycals can be used to prepare unsaturated 3-linked C-disaccharides. The incorporation of the alkene took place with one equivalent of glucal in the presence of boron-trifluoride etherate in 33% yield. The desired C-disaccharide was obtained by selective hydrogenation of the exocyclic double bond in the presence of an endocyclic one. 

More generally, cycloproparenes are available via dihalocarbene addition to cyclohexa-1,4-diene or synthetic equivalents, followed by base-induced twofold dehydrochlorination and aromatization. When the dichlorocarbene adduct of cyclohexa-1,4-diene, 7,7-dichlorobicyclo-[4.1.0]hept-.3-ene (3), was reacted with potassium /ert-butoxide in dimethyl sulfoxide a twofold elimination of hydrogen chloride occurred which was accompanied by migration of the resulting double bonds into the cyclohexene ring to give benzocyclopropene. This sequence, sometimes named Billups synthesis, provides the most convenient access to benzocyclopropene. ... 

If the alkene hydrogenation (step (c). Scheme 6.3) is a fast reaction, on the timescale of steps (a) and (b), it can serve as a reporter reaction for the lr(0) or Pt(0) formation, i.e., the kinetics of the overall reaction are represented only by the steps (a) and (b) in Scheme 6.3. Moreover, the sum of all three steps leads to a kineti-cally equivalent elementary step which relates the overall H2 consumption (cyclohexene) with the formation of lr(0) or Pt(0) NPs, the so-called pseudo-elementary step (d) (Scheme 6.3). 

Or consider another example. Cyclohexene and 1,3-hexadiene have the same molecular formula (CsHio). Both compounds react with hydrogen in the presence of a catalyst, but cyclohexene, because it has a ring and only one double bond, reacts with only one molar equivalent. 1,3-Hexadiene adds two molar equivalents ... 

Hydrogenation of benzene under pressure using a metal catalyst such as nickel results in the addition of three molar equivalents of hydrogen and the formation of cyclohexane (Section 14.3). The intermediate cyclohexadienes and cyclohexene cannot be isolated because these undergo catalytic hydrogenation faster than benzene does. 

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