Hydrogenation octalin

As previously described, a mixture of and J -octalins can be prepared by the reduction of naphthalene or Tetralin. Another route to this mixture is the dehydration of a mixture of 2-decalol isomers. This latter route has certain advantages in that one can avoid the handling of lithium metal and low-boiling amines. Moreover, 2-decalol is available commercially or can be prepared by the hydrogenation of 2-naphthol (5). In either case a comparable mixture of octalins is obtained, which can be purified by selective hydroboration to give the pure J -octalin (Chapter 4, Section III). 

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... 

Reduction of tetralin to octalin with lithium and ethylenediamine proceeds slowly, but if heated to 85°C it becomes violent, with rapid evolution of hydrogen. 

Because the cis-decalin molecule extends its two methine carbon-hydrogen bonds on the same side in contrast to frans-decalin, the carbon-hydrogen bond dissociation of adsorbed decalin would be advantageous to the cis-isomer on the catalyst surface (Figure 13.17). A possible reaction path by octalin to naphthalene in dehydrogeno-aromatization of decalin will be favored to the cis-isomer, since its alkyl intermediate provides the second hydrogen atom from the methine group to the surface active site easily. 

Tetrasubstituted Alkenes. Tetrasubstituted alkenes lacking electron-withdrawing substituents undergo facile ionic hydrogenation to alkanes in very good yields. Simple examples include 2,3-dimethyl-2-butene,208,214 1,2-dimethyl-cyclopentene, 1,2-dimethylcyclohexene,229 and A9(10)-octalin.126,204,212... 

ESR spectra for, 22 294, 301 as high-energy fuels, 18 2-4 hydrogenation course of, 18 6-8 equilibria, 18 7, 8 kinetic processes, 18 6, 7 experimental procedures, 18 19, 20 apparatus and methods, 18 20 materials, 18 20 mechanism of, 18 21-45 formation of isomeric decahydro-naphthalenes, 18 23-30 deuterogena-tion of - -octalin, 18 29 routes to trans isomers, 18 26-30 selectivity to trons-decalin, 18 24, 25 olefin intermediates, 18 30-45 dihydro-and hexahydronaphthalenes, 18 32, 33 analysis of products, 18 33 oc-tahydronaphthalenes, 18 34-45 analysis of products, 18 34 deu-... 

The formation of 1,9-octalin from fraras,[Pg.65]

Similarly Smith and Burwell (61) concluded that desorbed -octalin is a common intermediate in the formation of cis- and hydrogen-deficient species, possibly an allyl-77- complex (see Section III,C). 

Later, Weitkamp (102) isolated the octalins formed in the hydrogenation of methylnaphthalene, or naphthalene, over a platinum sup-... 

The nearly equal amount of cis and trans products formed from 1,5-dimethylcyclo-hexene is explained by the almost equal degree of hindrance of the homoallylic methyl group with the catalyst surface in the alternate adsorption modes.63 64 Another interesting example is the platinum-catalyzed hydrogenation of isomeric octalins.65-67 If syn addition to the double bond is assumed, in principle, both cis- and mms-decalin are expected to result from l(9)-octalin, but only the cis isomer from 9(10)-octalin. In contrast with these expectations, the isomers are produced in nearly the same ratio from both compounds. Transformation in the presence of deuterium revealed that most of the products contained three deuterium atoms. This was interpreted to prove that the very slow rate of hydrogenation of 9(10)-octalin [Eq. (11.9)] permits its isomerization to the 1(9) isomer. As a result, most of the products are formed through l(9)-octalin [Eq. (11.10)] ... 

Stereochemical differences were observed in the hydrogenation of 9(10)-octalin... 

The isomer ratio can be controlled by the steric size of the hydride donor silanes, and the highest selectivity is achieved when 9(10)-octalin itself is the hydride donor. None of the catalytic hydrogenations can produce such a high amount of the less stable cis isomer. 

The second approach is that developed to interpret the products of the reactions of octalins with deuterium [144] and is equally applicable to the reactions of mono- or di-unsaturated hydrocarbons with deuterium. Smith and Burwell [144] pointed out that, whereas the experimental deuterohydrocarbon distributions are obtained in terms of the number of deuterium atoms in the product hydrocarbon, the quantities of fundamental importance to the discussion of the mechanisms of catalytic reactions are the fractions of the hydrocarbon sample which have equilibrated with the surface deuterium—hydrogen pool. Thus, for example, in the reaction of buta-1 3-diene with deuterium, the product butenes consist of a series of species, butene-(/i, d)2, -(h, d)3,..., -(h, d)n in which 2,3. .., n positions... 

The synthesis of ( )-D-homotestosterone and ( )-progesterone has been accomplished via a now classical procedure involving the use of an isoxazole as an annelating agent (67JA5464). The enolate (424), prepared from 10-methyl-A1,9-octalin-2,5-dione, was alkylated by the 4-chloromethylisoxazole (425). The octalindione (426) was treated sequentially with one equivalent of sodium borohydride, hydrogenated, hydrogenolyzed and refluxed with sodium methoxide and then with sodium hydroxide to afford the crystalline enone (427). 

The possibility that isomerization may effect the selectivity is important to note. A convenient method of removing 1,9-octalin from a mixture of the 1,9- and the 9,10-octalins is to hydrogenate the mixture over a Pt catalyst. Pd is ineffective because it is more active than Pt in catalyzing the interconversion of the isomers, eqn. (5) (procedure suggested by Hussey given in ref. 30). 

Scheme 9.5 Hydrogenation of naphthalene note, the other possible octalin isomers are usually converted to the two shown by doublebond migration, since the C=C bond is most stable when most heavily substituted.

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