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Synthesis and stereochemistry of some 9, 10-disubstituted cis-decalins Scott, William Bruce

Abstract

The application of low temperature nuclear magnetic resonance (n. m. r.) spectroscopy to the determination of the barrier heights to interconversion in compounds which contain one and two flexible six-membered rings is reviewed. Although the barrier heights in cyclohexane and its derivatives have been experimentally determined, similar studies in the cis-decalin system have (until very recently) not been successful. Consideration is given, therefore, to the preparation of a number of cis-9, 10-disubstituted decalin derivatives, which will act as model compounds for a further study in the problem of the barrier height to ring interconversion in the cis-decalin system. Various attempts to synthesize a novel model compound, tricycle [4. 4. 4. 0] tetradecane, are described. Partial success has been achieved in that a small but demonstrable amount of tricycle [4. 4.4. 0]-3, 8-tetradecadiene has been synthesized in a ten step reaction sequence, starting from acetylenedicarboxylic acid. A Diels-Alder condensation of this compound with two mole-equivalents of 1, 3-butadiene gave Δ² ⁶-hexalin-9,10-dicarboxylic anhydride. Lithium aluminum hydride reduction of this compound gave cis-9, 10-bis(hydroxymethyl)-Δ² ⁶ -hexalin, which was converted to its dimesylate derivative on treatment with methanesulfonyl chloride in pyridine. Reaction of the dimesylate derivative with sodium cyanide in N-methyl-2-pyrrolidinone gave cis-9, 10-bis(cyanomethyl)-Δ² ⁶-hexalin. Alkaline hydrolysis of the latter gave cis-9,10-bis(carboxymethyl)-Δ² ⁶-hexalin, which was converted to its dimethyl ester on treatment with diazo- methane in 1, 2-dimethoxyethane. Lithium aluminum hydride reduction of the dimethyl ester gave cis-9,10-bis(2-hydroxyethyl)Δ² ⁶-hexalin. Treatment of the dialcohol with methanesulfonyl chloride in pyridine gave cis-9, 10-bis(2-mesyl-oxyethyl)-Δ² ⁶-hexalin. Reaction of the dimesylate with sodium iodide in acetone gave cis-9, 10-bis(2-iodoethyl)-Δ² ⁶-hexalin. Treatment of this compound with n-butyllithium in diethyl ether and in heptane gave a mixture of cis-9-ethyl-10- vinyl-Δ² ⁶-hexalin and tricyclo[4. 4.4. 0]-3, 8-tetradecadiene (minor product). Attempts to improve the yield of the tricyclic compound, using zinc and magnesium as coupling reagents, were unsuccessful. The syntheses of other desired model compounds are described. Thus, cis-9, 10-dimethyl-Δ²-octalin and -Δ² ⁶-hexalin were prepared from their cis- 9, 10-bis(mesyloxymethyl)- analogs on treatment of the latter compounds with sodium iodide in N, N-dimethylformamide, followed by the treatment of the respective product diiodides with lithium aluminum hydride in 1, 2-dimethoxyethane. cis-9,10- Dimethyldecalin was prepared from cis-9, 10-dimethyl-Δ² ⁶-hexalin by catalytic hydrogenation of the latter. In addition, treatment of cis-9, 10-bis(hydroxymethyl)- decalin and -Δ²-octalin with p-toluenesulfonic acid in benzene yielded 12-oxa- tricycle [4. 4. 3. 0] tridecane and -3-tridecene, respectively. 12-Oxatricyclo [4. 4. 3. 0] -3, 8-tridecadiene was isolated as a by-product from the reaction of cis-9, 10-bis- (mesyloxymethyl)-Δ² ⁶-hexalin with sodium cyanide in N-methyl-2-pyrrolidinone, as was 12-amino-11-cyanotricyclo [4. 4. 3. 0]-3, 8, 11-tridecatriene. All of the new compounds have been characterized by means of infrared, ultraviolet, and n. m. r. spectroscopy, mass spectrometry, and microanalysis, where applicable. Preliminary investigations of the barrier heights to interconversion in cis-9, 10-dimethyldecalin and 12-oxatricyclo [4. 4. 3. 0] tridecane are described. Quantitative kinetic data could not be obtained from the low temperature (0 to -60°) n. m. r. spectra of the former, since no broadening of the ring proton resonance peak was observed. On the other hand, the latter compound gave n. m. r. spectra in which the ether ring proton resonance peak broadened considerably as the sample temperature was lowered. From these spectra a value of the energy of activation (Ea) of 8. 4 ± 2 kcal. /mole was calculated for the interconversion process in 12-oxatricyclo [4. 4. 3. 0] tridecane.

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