Methylcyclohexene, hydrogenation

Hydrocarbons with easily abstractable hydride ion such as 1,4-cyclohexa-diene,227 cycloheptatriene,223 or compounds possessing tertiary or benzylic hydro-gen217,218,223 230 231 are suitable substitutes for silanes. In fact, this was the case in the first ionic hydrogenation observed by Ipatieff and coworkers. In an attempt to carry out alkylation of p-cymene with 3-methylcyclohexene, hydrogenation of the latter occurred, where p-cymene was the hydride ion source ... 

The rate of transfer hydrogenation also varies markedly with donor structure. For cyclohexene, 1 -methylcyclohexene, l-methyl-4-isopropyl-cyclohexene,and l-methyl-4-f-butyIcycIohexene as donor in the above hydrogenations, after 1 min the reduction was 11, 78, 99, and 99% complete, respectively (97). 

Solvents can have a large influence on the extent of double-bond migration (6). The factors involved are complex as shown in the hydrogenation of methylenecyclohexane, 3-methylcyclohexene, and 4-methylcyclohexene to methylcyclohexane in benzene-ethanol, in peniane, and in ethanol over 5% Pd, 5% Pt, and 5% Rh-on-carbon. The amount of isomerized 2-methylcy-clohexene was measured ai 25% completion and, depending on the system,... 

A quantitative comparison of metals in the hydrogenation of vinyl ethers has been made, The extent of hydrogenolysis in hydrogenation of l-ethoxy-3-methylcyclohexene decreased in the order Pt Os > Rh Ir > Pd > Ru U24e)-, in the case of ethyl 4-methyl-1-cyclohexenyl ether, the order was Pt Ir > Rh > Os Ru Pd (124d). In ethanol, ketal formation is a... 

Treatment of an alkyl halide with a strong base such as KOH yields an. alkene. To find the products in a specific case, locate the hydrogen atoms on each carbon next to the leaving group. Then generate the potential alkene products by removing HX in as many ways as possible. The major product will be the one that has the most highly substituted double bond—in tints case, 1-methylcyclohexene. 

Ion 21 can either lose a proton or combine with chloride ion. If it loses a proton, the product is an unsaturated ketone the mechanism is similar to the tetrahedral mechanism of Chapter 10, but with the charges reversed. If it combines with chloride, the product is a 3-halo ketone, which can be isolated, so that the result is addition to the double bond (see 15-45). On the other hand, the p-halo ketone may, under the conditions of the reaction, lose HCl to give the unsaturated ketone, this time by an addition-elimination mechanism. In the case of unsymmetrical alkenes, the attacking ion prefers the position at which there are more hydrogens, following Markovnikov s rule (p. 984). Anhydrides and carboxylic acids (the latter with a proton acid such as anhydrous HF, H2SO4, or polyphosphoric acid as a catalyst) are sometimes used instead of acyl halides. With some substrates and catalysts double-bond migrations are occasionally encountered so that, for example, when 1 -methylcyclohexene was acylated with acetic anhydride and zinc chloride, the major product was 6-acetyl-1-methylcyclohexene. ... 

In summary, partial hydrogenation of anisole to 1-methylcyclohexene by polyoxoanion-stabilized Rh(0) nanoclusters is very modest but could in the future be an interesting additive study in the monocyclic arene hydrogenation research area. 

The most common rearrangement reaction of alkyl carbenes is the shift of hydrogen, generating an alkene. This mode of stabilization predominates to the exclusion of most intermolecular reactions of aliphatic carbenes and often competes with intramolecular insertion reactions. For example, the carbene generated by decomposition of the tosylhydrazone of 2-methylcyclohexanone gives mainly 1- and 3-methylcyclohexene rather than the intramolecular insertion product. 

To add another complication recently, (R)-(—)-10-methyl-A1(-9)-octalin (7) has been prepared and its hydrogenation studied over Pt, Pd, and Rh catalysts.91 Like the apopinenes and the (R)-(—)-4-methylcyclohexene, this R enantiomer may undergo double bond migration to its 5 enantiomer, which... 

Trisubstituted Alkenes. With very few exceptions, trisubstituted alkenes that are exposed to Brpnsted acids and organosilicon hydrides rapidly undergo ionic hydrogenations to give reduced products in high yields. This is best illustrated by the broad variety of reaction conditions under which the benchmark compound 1-methylcyclohexene is reduced to methylcyclohexane.134 146,192 202 203 207-210 214 234 When 1-methylcyclohexene is reduced with one equivalent of deuterated triethylsilane and two equivalents of trifluoroacetic acid at 50°, methylcyclohexane-... 

A particularly clear example is shown in Fig. 8, the hydrogenation of 4-ler<-butylmethylenecyclohexane (64). In this instance, the most likely initial product of isomerization is the endocyclic isomer, 4-leri-butyl-l-methylcyclohexene, which would yield mainly trans-4-tert-butyl-l-methylcyclohexane. Further, the exocyclic olefin, the original substrate, is reduced selectively in competition with its endocyclic isomer so that the latter cannot he an intermediate in the hydrogenation of the former. 

Fig. 17. Preferred conformations of the transition state which yields the half-hydrogenated state from a 4-substituted methylcyclohexene and a methylenecyclohexane.

Methylcyclohexene reacts with hydrogen chloride to form two products. Draw a... 

Hydrogenolysis of epoxides to alcohols by catalytic hydrogenation over platinum requires acid catalysis. 1-Methylcyclohexene oxide was reduced to a mixture of cis- and /ranj-2-methylcyclohexanol [652]. Steroidal epoxides usually gave axial alcohols stereospecifically 4,5-epoxycoprostan-3a-ol afforded cholestan-3a,4/J-diol [652 ]. 

Variation of the olefin also has an effect on kaaa//cab3. For example, the irradiation of benzophenone in 1-methylcyclohexene gives a moderate yield of the oxetane (even though there are three more allylic hydrogens on this olefin as compared to cyclohexene). Isobutylene too gives much higher yields of the oxetane than 1-butene.37,66 The controlling factor in these cases may be the increased stability of the diradical intermediates. 

Halofluorinations take place, as a rule, regioselectively (Markovnikov addition), the olefinic carbons can be substituted with a variety of substituents ranging from alkyl or aryl groups to different electron-withdrawing functions see for example refs 31 and 178-180. Bromo-fluorination of 4-/m-butyl-l-methylcyclohexene with /V-bromosuccinimide in 70% hydrogen fluoride/pyridine gave two stereoisomers 1 and 2.181... 

In turn, our archive shows that 3-methylcyclopentene has been reported to be 7.2 2.1 kJmol-1 more stable than the 4-isomer. Interestingly, hydrogenation calorimetry (cf Reference 67) shows the 1,3-isomer difference to be 14.1 Id mol 1 but no data is available to compare the 3- and 4-isomers. We also note that 1-methylcyclohexene (as liquid) is found to be 6 4 kJ mol-1 more stable than its 4-isomer as shown by the archival enthalpy of formation of the former and the measurement of B. Lebedev and H. Smirnova, Macromol. Chem. Phys., 195, 35 (1994). 

The effect of different metals on the stereochemistry was studied149,150,151 in the hydrogenation of 4-ferf-butyhnethylenecyclohexane (9). Whereas Pt, Rh, Ir and Ru yield predominantly the cis isomer, fraws-l-terf-butyl-4-methylcyclohexane is the main product on Pd. The stereochemical behavior of 9 was very similar to that found for the hydrogenation of the isomeric 4-ferf-butyl-l-methylcyclohexene (10) (increasing cis selectivity... 

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