Rearrangement adamantanes

Rearrangement, acid-catalyzed, of cyclohexanone diallyl acetal to 2-allylcyclohexanone, 42,14 of e do-tetrahydrocyclopentadiene to adamantane, 42,9 pinacol, of 1,2-indanediol, 41, 53... 

It was mentioned above that even alkanes undergo Wagner-Meerwein rearrangements if treated with Lewis acids and a small amount of initiator. An interesting application of this reaction is the conversion of tricyclic molecules to adamantane and its derivatives. It has been found that all tricyclic alkanes containing 10 carbons are converted to adamantane by treatment with a Lewis acid such as AICI3. If the substrate contains more than 10 carbons, alkyl-substituted adamantanes are produced. The lUPAC name for these reactions is Schleyer adamantization. Two examples are... 

Schleyer s Lewis acid-catalyzed rearrangement method, which is based on diamondoid thermodynamic stability during carbocation rearrangements, has had little or no success in synthesizing diamondoids beyond triamantane. In recent years, outstanding successes have been achieved in the synthesis of adamantane and other lower molecular weight diamondoids [42 9]. Some new methods have been developed and the yield has been increased to 60%. 

When 2-ethynyl-2-hydroxyadamantane (31) was treated with 95% formic acid or dilute sulfuric acid only a Meyer-Schuster rearrangement took place to give 95% of 2-(formylmethylene)adamantane (32) (equation 10). No Rupe rearrangement took place29. 

It is interesting to mention the cyclizations of allene systems which are accompanied by rearrangements. Protonation of the bis-cumulene 74 by 5% H2SO4 in aqueous acetone produces the adamantane derivative 75 in 95% yield (equation 28)43. 

The one-electron oxidation of iV-benzylphenothiazine by nitric acid occurs in the presence of /i-cyclodextrin, which stabilizes the radical cation by incorporation into its cavity. The reaction is inhibited by adamantane, which preferentially occupies the cavity. Novel Pummerer-type rearrangements of / -sulfinylphenyl derivatives, yielding /7-quinones and protected dihydroquinones, and highly enantioselective Pummerer-type rearrangements of chiral, non-racemic sulfoxides have been reviewed. A comprehensive study has demonstrated that the redox potential for 7- and 8-substituted flavins is linearly correlated with Hammett a values. DFT calculations in [3.3.n]pro-pellanes highlight low ionization potentials that favour SET oxidative cleavage of the strained central C-C bond rather than direct C-H or C-C bond attack. Oxidations and reductions in water have been reviewed. ... 

A single trifluoromethyl group is sufficient to prevent rearrangement [perfluoro(l-methyl-adamantane) is obtained from l-(trifluoromethyl)adamantane in 65 % yield], but two fluorines are not as 1,3-difluoroadamantane undergoes rearrangement.53... 

All Cio polycylie hydrocarbons under strongly acidic conditions undergo a unique isomerization to give adamantane.32-34 The adamantane rearrangement was discovered by Schleyer in connection with the catalytic interconversion of endo- and evo-trimethylenenorbomane 35-37... 

The interconversion of possible CioH16 isomers to adamantane, the thermodynamically most stable isomer, is a very complex system. It involves practically thousands of carbocationic intermediates via 1,2-hydride, alkyde shifts. The interconversion possibilities were summarized in a complex map of rearrangement graph ( adamantaneland ).45,46 The adamantane rearrangement is now recognized to be general for polycyclic hydrocarbons with the formula C4 +6H4 +12 (n = 1,2,3). 

Catalysis. The isomerization of cyclopropane to propylene and the rearrangement of protoadamantane to adamantane were studied on HY zeolite and samples of materials A and B. 

The rearrangement of protoadamantane to adamantane was studied on HY zeolite and those samples of materials A and B produced by reaction with TMS at 400°C. The catalysts (0.1 gram) were activated at 600°C for 6 hours in vacuo and were transferred to a flow system where the reaction was carried out at 240° C under N2 at atmospheric pressure. The reaction is totally selective, giving 96.7% and 42.5% conversion to adamantane on HY and the A material, respectively, but only 7.2% conversion on the B material. 

Catalytic and Electron Transfer Properties. The isomerization of cyclopropane on HY zeolites activated at temperatures less than 600° C is attributed to catalysis by Bronsted acid sites (12, 13), and the activation temperature for maximum activity was in the range 300°-400°C (13). On the other hand, rearrangement of protoadamantane to adamantane proceeds by hydride ion abstraction at Lewis acid sites (lfy. Materials B, therefore, appear to have good Bronsted activity (Figure 5) and in view... 

Like adamantane,6 diamantane (also known as congressane4), the second member of the diamond family, may also be prepared by aluminum halide-catalyzed isomerization. A variety of starting materials have been shown to give diamantane,2 4,7,8 but the very best results are obtained by the present procedure2 8 starting with Binor-S.2,3,9 Diamantane may be converted to a variety of functionalized derivatives.2,5,10,11 4-Methyldiamantane may also be prepared by rearrangement.10... 

Monitoring by GC provided evidence [25] for several intermediates in the isomerisation of tetrahydrodicyclopentadiene (39) to adamantane (40), Scheme 2.15, a thermodynamically controlled process (discovered serendipitously) [26]. Molecular mechanics calculations indicated that the slow step of the rearrangement could occur prior to formation of exo-41, which rearranges in a few minutes to 40 on treatment with AlBr3 in CS2 at 25°C. When the reaction of exo-41 was conducted at — 10°C and monitored by GC over a period of 100 minutes, the presence of two additional intermediates (42 and 43) was revealed [25]. 

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