C/s-Decalins

Problem 4.20 Which isomer is more stable, c/s-decalin or fram-decalin Explain. 

Other successful selective oxidations of hydrocarbons by Cr(VI) have been reported— for example, the oxidation of c/s-decalin to the corresponding alcohol—but careful attention to reaction conditions is required. 

Reported vapor pressures of c/s-decalin at various temperatures and the coefficients for the vapor pressure ... 

FIGURE 2.1.1.2.14.3 Logarithm of vapor pressure versus reciprocal temperature for c/ s-decalin. 

Among the most important of the bicyclic hydrocarbons are the two stereoisomeric bicyclo[4.4.0]decanes, called cis- and frans-decalin. The hydrogen atoms at the ring junctions are on the same side in c/s-decalin and on opposite sides in mms-decalin. Both rings adopt the chair conformation in each stereoisomer. 

Exercise 12-27 The equatorial form of methylcyclohexane is 1.5 kcal mole-1 more stable than the axial form because the axial form has steric hindrance between the methyl and two hydrogens, one in the 3- and the other in the 5-position. Knowing that c/s-decalin is about 2 kcal mole-1 less stable than frans-decalin, what would you estimate for the relative stabilities of cis- and frans-9-methyldecalin (numbering as in Figure 12-22) ... 

Figure 12-22 Representation of c/s-decalin showing nonbonded interactions (shaded areas). The numbering of the decalin ring is the currently accepted convention, which is not the same as the numbering system used generally for bicyclic systems, as described in Section 12-8.

Figure 12-24 Ring inversion in c/ s-decalin, which takes a substituent from the equatorial to the axial position. In both conformations, each ring is a chair form. You should check this process with ball-and-stick models.

First a brief rentin 1 of the conformation of c/s-decalins (see Chapter 18). Unlike frans-decalins, which are rigid, th caii flip rapidly between two all-chair conformations. During the flip, all... 

If either of these products is reduced with hydrogen and a Pd catalyst (the alcohol is first made into a tosylate), the c/s-decalin is formed. We saw a few pages back that the same kind of enones can be reduced with lithium metal in liquid ammonia and that then the more stable trans-decalm... 

In order to obtain high enantioselectivities it seems to be important that the reactions proceed via cationic intermediates (e.g. 24) to disfavor the partial dissociation of the chiral ligand. For this reason, silver salts are added to reactions of vinyl-iodides. These reactions are best performed in Al-methylpyrrolidone (NMP) as a solvent. As the examples shown in Scheme 9 demonstrate, both c/s-decalin [12] and cA-hydrindane [13] derivatives can be obtained in useful yields and enantiomeric purities. 

Onocerane triterpenes. This reagent was used in the first synthesis of the unsym-metrieal a, -onoceradiencdione (8) for cyclization of two famesol derivatives, (2) and (6), to A/B-rra/i.r, 9/IO-c(.s decalin systems. 

Methyl-as-deealins. The reaction of 3-methyl-4-methylcnc-2-cycIohexen-one (2) with 1 in DMSO with KF as catalyst (55-60°, 2 days) leads to a mixture of the stereoisomeric diketo diesters 3 and 4. The reaction involves a double Michael addition. Both products are converted to the same diketone (5) on decar-bomethoxylation. 9-Methyl-c/s-decalin (6) was obtained from 5 by standard reactions. 1,9- and 4,9-Dimethyl-cis-decalin were also prepared in the same way. ... 

We saw in Problem 4.20 that c/.s-decalin is less stable than fm/rs-decalin. Assume that the l/t-diaxial interactions in frnn.s-decaiin are simiiai to those in axial methylcyclohexane [that is, one Cl h —>11 interaction costs 3.8 kj/rnol (0.9 kcal/mol), and calculate the magnitude of the energv difference between d.s- and /wns-decalin. 

A Lewis acid-mediated two-fold asymmetric Michael addition allows access to c( s-decalin derivatives. The reaction of the trimethylsilylenol ether of acety Icyclohexene with phenylmenthyl acrylate in the presence of Diethylaluminum Chloride (eq 7) yields the decalone in 64% yield (70% de). This has been shown not to be a Diels-Alder reaction. If the reaction is worked-up early, the initial Michael adduct can be isolated. ... 

The solution to this problem is quite easy to visualize if the tricyclic structure II is looked upon as a c/s-decalin skeleton to which an extra C-C bond between carbons in different rings has been added. That this bond is made at the expense of the cyclopropane ring of I becomes obvious not only because of the absence of this three membered unit in II, but also because the other functions (C=C and C=0) appear in the product without any change other than the isomerization of the double bond. 

During the enantioselective synthesis of (3aR,4R,7aS)-4-hydroxy-7a-methylperhydro-1-indenone, a suitable CD-ring fragment for vitamin D-anaiogs, M. Vandewalle et al. realized that the hydroboration/oxidation of (1,1)-ethylenedioxy-8a-methyl-1,2,3,4,6,7,8,8a-octahydronaphtalene led to a c/s-decalin structure instead of the literature reported trans-fusion." ... 

Figure 5.4 First-derivative EPR spectra obtained after y-irradiation of neat c/s-decalin-d,g (a) and of c/s-decalin-d,j containing 1 mol% 1-bromooctane (b), 2-bromooctane (c) and 3-bromooctane (d). The dashed...

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