1- Methylcyclohexene, reduction

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). 

REDUCTIVE CLEAVAGE OF ALLYLIC ALCOHOLS, ETHERS, OR ACETATES TO OLEFINS 3-METHYLCYCLOHEXENE... 

Treatment of l-[2-(2-methoxy-5-isopropylphenyl)-l-hydroxyethyl]-2,6,6-tri-methylcyclohexene with triethylsilane and boron trifluoride etherate in dichloro-methane at —10° leads to its reduction to 2-(2,6,6-trimethyl-l-cyclohexenyl)-l-(2-methoxy-5-isopropylphenyl)ethane in 69% yield (Eq. 36).174... 

In addition to the present method,2 1-amino-1-methylcyclo-hexane has been synthesized by the following procedures Ritter reaction, e.g., with 1-methylcyclohexanol (76%, 67%)3i 4 or 1-methylcyclohexene (35%,) 4 5 Hofmann reaction with 1-methyl-cyclohexanecarboxamide (80% as hydrochloride) 6 reduction of 1-methyl-l-nitrocyclohexane (63%) 6 Schmidt reaction with 1-methylcyclohexanecarboxylic acid (42%).6... 

Compounds 16 and 19 each deliver the expected six alcohols after reduction of the primarily formed hydroperoxide mixtures as a result of an oxygen attack on the trisubstituted A1 double bonds of these molecules. The ratio of tertiary/secondary hydroperoxides (or alcohols) is about 44 56, as has also been found with 1-methylcyclohexene (30)13S while open-chain olefins such as trimethylethylene (S3), 1,1-dimethyl-2-ethylethylene (id), 2,6-dimethyl-2-octene (39), myrcene (42), / -citronellol (45), linalool (48), and l,l-dimethyl-2-benzylethylene (51) give ratios of tertiary/secondary hydroperoxides between 54 46 and 60 40.104-1 7 7 1 79 The slight deviations from 1 1 ratios in all these cases are probably due to stereochemical rather than electronic effects exerted by the olefins on the reaction with oxygen. 

In this synthesis the geometry of the acyclic double bonds is controlled through their formation as part of the thiane ring. Thiacyclohexanone (711) was converted to 4-thia-l-methylcyclohexene by reaction with methylmagnesium iodide and subsequent dehydration. Metallation of (712) with s-butyllithium and alkylation of the anion with the epoxide (713) gave a tertiary alcohol which was dehydrated to yield (714). A second alkylation of (714) with trails-4-chloro-3-methyl-2-butene 1-oxide (715) completed the carbon skeleton of the Cis juvenile hormone. Reduction of (716) with lithium in ethylamine and then desulfurization with Raney nickel led to trienol (717), a product converted previously to (718). 

Some other catalytic events prompted by rhodium or ruthenium porphyrins are the following 1. Activation and catalytic aldol condensation of ketones with Rh(OEP)C104 under neutral and mild conditions [372], 2. Anti-Markovnikov hydration of olefins with NaBH4 and 02 in THF, a catalytic modification of hydroboration-oxidation of olefins, as exemplified by the one-pot conversion of 1-methylcyclohexene to ( )-2-methylcycIohexanol with 100% regioselectivity and up to 90% stereoselectivity [373]. 3. Photocatalytic liquid-phase dehydrogenation of cyclohexanol in the presence of RhCl(TPP) [374]. 4. Catalysis of the water gas shift reaction in water at 100 °C and 1 atm CO by [RuCO(TPPS4)H20]4 [375]. 5. Oxygen reduction catalyzed by carbon supported iridium chelates [376]. - Certainly these notes can only be hints of what can be expected from new noble metal porphyrin catalysts in the near future. 

Both cis- and tram-isomers were formed from 1-methylcyclohexene in trichloroethylene, as deduced from the complexity of the H-NMR spectrum of the isolated product (21 %)31. Different physical properties and stereochemistry were assigned to the adduct prepared from 1-phenylcyclohexene in the same conditions by different authors31,32, but the possibility that different dimers were isolated by homospecific and heterospecific dimerization should be considered, syn Addition was claimed in one of these reports, since the presumed cis adduct was converted to m-2-phenylcyclohexanamine by reduction with lithium aluminum hydride31. However, oxidation of the tram-adduct afforded the corresponding nitro derivative, whose dipole moment agreed with the value calculated for the tram-product32. 

The stereospecific conversion of cyclohexene into the corresponding amido selenide 54 is illustrated in Scheme 8. These amidoselenenylation reactions are commonly employed for the preparation of allylic and saturated amides by oxidative or reductive deselenenylation. Propionitrile, butyronitrile, benzonitrile and ethyl cyanoacetate may be used in place of acetonitrile. Styrene gave poor results and other electron-rich olefins such as 1-methylcyclohexene or 2,3-di-methylbut-2-ene did not give the amidoselenenylation products. The reaction can also be effected starting from the hydroxy- or methoxyselenenylation products of alkenes, in the presence of water and trifluoromethanesulfonic acid in this case the nitriles are used in stoichiometric amounts [48c]. This methodology was employed to prepare the amidoselenenylation products of styrene, 55, and of electron-rich olefins. It was necessary, however, to replace the phenyl-... 

In the absence of a laboratory or industrial pressure vessel, catalytic hydrogentransfer is a viable alternative. Here, the nitro compound is stirred in a solvent with a catalyst, commonly 1% platinum on carbon, in the presence of a hydrogen donor such as hydrazine, sodium formate (sodium methanoate) or methylcyclohexene (Scheme 7.6). In the case of hydrazine, interaction at the catalyst surface produces the reductant, hydrogen, and nitrogen. Toluene is the by-product when methylcyclohexene is used. 

Electrochemical methods for the reduction of aromatic substrates utilizing ammonia and amines as solvents with lithium salts as electrolytes have been successful. Toluene was reduced to the 2,5-dihydro derivative in 95% yield in methylamine-lithium chloride if an undivided cell was used, while a 53 47 mixture of 3- and 4-methylcyclohexenes was formed in a divided cell.. Of greater interest, however, are attempts to achieve these reductions in aqueous media. In one experiment utilizing a two-phase mixture of substrate in aqueous tetra-n-butylammonium hydroxide and a mercury cathode, anisole was reduced on a preparative scale (15 g) to its 2,5-dihydro derivative in 80% yield. The optimal temperature for most reductions appeared to be 60 °C and under these conditions, even suspensions of high molecular weight substrates could be successfully reduced, e.g. steroid (226) afforded a >90% chemical yield of (227). Much higher coulombic yields were obtained when a small amount of THE was added to the mixture, however. 

High catalytic activities, with turnovers of up to 9(X) cycles min , is displayed in the transfer hydrogenation of a,p-unsaturated ketones, such as benzylideneacetone and chalcone, using 2-propanol and catalytic amounts of [Ir(3,4,7,8-Me4-phen)COD]Cl (phen = 1,10-phenanthroline COD = 1,5-cyclo-octadiene) in a weakly alkaline medium. Other Ir-chelated complexes are also active catalysts in this reaction, with over 95% selectivity for the 1,4-reduction mode. Divalent lanthanide derivatives, such as Sml2 or Ybh in stoichiometric quantities, in THF and t-butyl alcohol or methanol reduce ethyl cinnamate and cinnamic acid to give the saturated derivatives. " Similarly, 3-methylcyclohexenone is reduced to 3-methylcyclohexen-l-ol in 67% yield, but a,p-unsaturated aldehydes are nonselectively reduced with these systems. 

In contrast to the reductive cleavage of 1-methylcyclohexene epoxide with LiAlH4 or, better, with LiEtjBH to produce 1-methylcyclohexanol, reduction of the epoxide with sodium cyanoborohydride in the presence of boron trifluoride etherate furnishes cE-2-methylcyclohexanol. In this case, complexation of the epoxide oxygen with the Lewis acid BF3 now directs hydride addition to the more substituted carbon, which can better sustain the induced partial positive charge. 

Treatment of toluene in methylamine with 4 equivalents of lithium effects reduction to a mixture of methylcyclohexenes found by VPC analysis to contain 59% of 1-methylcyclohexene (V) and 41% of 3- and 4-methylcyclohexene. The reactions... 

Palladium also efficiently catalyzes the isomerization of cyclic olefins (15, 17, 19) 1,1-dimethylcyclohexene isomerizes to a small extent to the less stable 2,3-isomer 17), but 2-methylmethylenecyclohexane is rapidly isomerized, and has indeed disappeared after 30% hydrogenation, It is significant that the 2,3-dimethylcyclohexene is the major initial product, and this subsequently passes to the stabler 1,2-isomer (17). 4-fer<-Butylmethylenecyclohexane similarly is converted rapidly to the stabler 4-palladium-charcoal, 4-methylmethylenecyclohexane isomerizes completely to 1,4-dimethylcyclohexene, which itself does not isomerize (19). Table XII shows the olefin compositions which result after partial reduction of a number of related olefins there are two comparably stable isomers (C and D), and these are both popular, but it is likely that neither of the two kinds of distributions shown are true equilibrium distributions. J -octalin isomerizes to J -octalin over palladium-charcoal (19). The stereochemical analysis of hydrogenations over palladium is substantially complicated by this extensive isomerization. 

Furthermore, dehydration of the alcohols formed to 4-methylcyclohexene (4-Me-ENE) was observed in the gas phase, while no trace of dehydrated products could be detected in liquid phase MPV reductions. The somewhat higher temperature of 100 °C compared with 85 °C for the liquid-phase experiments, could not explain this behaviour, since lowering the temperature to 85 °C still resulted in a 4-Me-ENE selectivity of approximately 10 % over Ti-beta. The remarkable differences in selectivity between the gas- and liquid-phase MPVO reaction induced us to study the evolution of products as a function of the temperature, in the reduction of 4-methylcyclohexanone. From Fig. 4 it can be seen that the selectivity to the cis-alcohol decreases at higher temperatures initially the selectivity to the trans-alcohol increases but at higher temperatures dehydration to 4-methylcyclohexene becomes the major reaction. At still higher temperatures (> 200 °C) the 4-methylcyclohexene is subsequently isomerised to the more stable 1-methylcyclohexene. 

Reduction of epoxides. The reaction of diborane alone with epoxides is complicated. Thus 1,2-butylene oxide requires 48 hrs. and gives a mixture of butanols (96% 2-butanol and 4% 1-butanol) in only 48% yield. The reaction with trisub-stituted epoxides is even more complicated and only trace amounts of simple alcohols are formed. Brown and Yoon1 found that the presence of trace amounts of sodium or lithium borohydride greatly enhances the rate of reaction and modifies the course to give predominantly anti-Markownikov opening of the epoxide ring. Thus 1-methylcyclohexene oxide is reduced mainly to m-2-methylcydohexanol ... 

Silane hydrides can be used for the reduction of carbonyls and alkenes. Reaction of methylcyclohexene with a mixture of triethylsilane (EtsSiH) and trifluoroacetic acid (CF3CO2H) reduced the alkene moiety to give methylcyclohexane in 72% yield. 2 Under the same conditions, however, 1-pentene was not reduced. More commonly, this reagent is used for reduction of conjugated carbonyls, probably via formation of a silyl enolate (secs. 9.2, 9.3.B) as in the reduction of cyclohexenone to cyclohexanone in 85% yield with Ph2SiH2. Addition of transition metals such as ZnCl2, or copper salts to the silane facilitates the reduc-tion,594 as in the conversion of 576 to 577 in 96% yield. ... 

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