Adamantanes, formation

The skeletal isomerization of tetrabydrodicyclopentadiene into adamantane is an example of a very complex rearrangement diat is commercially carried out over strong Lewis acids with a hydride transfer initiator. The reaction can be catalyzed by rare earth (La, Ce, Y, Nd, Yb) exchanged faujasites (Scheme 1) in a Hj/HCl atmosphere at 25(yX3. Selectivities to adamantane of up to 50% have been reported, when a metal fimction, such as Pt, capable of catalyzing hydrogenation is added [54]. Initially acid catalyzed endo- to exo- isomerization of tetrahydro-dicyclopentadiene takes place and then a series of 1,2 alkyl shifts involving secondary and tertiary carbonium ions leads eventually to adamantane[55]. The possible mechanistic pathways of adamantane formation from tetrahydro-dicyclopentadiene are discussed in detail in ref [56]. 

A special case of shape selectivity should be mentioned at the end of this section, i.e., the formation of adamantane from 1-hexene in the pores of SAPO-34 [268]. The intra crystalline cavities in the chabazite structure seem to be especially suited to catalyze adamantane formation with high selectivity at temperatures of around 500 K. However, the narrow pore openings do not allow the product to leave the catalyst. High concentrations of adamantane were isolated by dissolving the molecular sieve in HF. 

Rearrangement cf an arylprotoadamantanol (1) in boiling formic acid aifords the corresponding adamantane formate ester (2).5... 

Find the MM3 enthalpy of formation of 1- and 2-methyladamantane. Use the Rings tool and the adamant option to obtain the base structure of adamantane itself. Use the Build tool to add the methyl group. 1-Adamantane is the more symmetrical structure of the two isomers. 

Protonation of formic acid similarly leads, after the formation at low temperature of the parent carboxonium ion, to the formyl cation. The persistent formyl cation was observed by high-pressure NMR only recently (Horvath and Gladysz). An equilibrium with diprotonated carbon monoxide causing rapid exchange can be involved, which also explains the observed high reactivity of carbon monoxide in supera-cidic media. Not only aromatic but also saturated hydrocarbons (such as isoalkanes and adamantanes) can be readily formylated. 

Tnfluoroacetic anhydnde in a mixture with sulfuric acid is an efficient reagent for the sulfonylation of aromatic compounds [44] The reaction of benzene with this system in nitromethane at room temperature gives diphenyl sulfone in 61% yield Alkyl and alkoxy benzenes under similar conditions form the corresponding diaryl sulfones in almost quantitative yield, whereas yields of sulfones from deactivated arenes such as chlorobenzene are substantially lower [44] The same reagent (tnfluoroacetic anhydride-sulfunc acid) reacts with adamantane and its derivatives with formation of isomeric adamantanols, adamantanones, and cyclic sultones [45]... 

A second example of the use of esters as enolates is the formation of Meerwein s ester, an intermediate in the synthesis of substituted adamantanes (6). Dimethyl... 

In this instance, adamantane was present to promote interaction of peptides through its hydrophobicity, but its attachment did not hinder fibril formation. It might be possible to chemically or biologically derivatise this group before being introduced to the peptide, or to select another hydrophobic component that could be suitably modified and attached to the peptide. This research also highlights the feasibility of creating peptide arrays comprised of several different sequences. 

In Table IV we report the available enthalpies of formation, sublimation, and combustion of methyl-adamantanes, dimethyl-adamantane, trimethyl-adamantane, and tetramethyl-adamantane and compare them with the same properties of adamantane as measured by various investigators [29, 30]. Also reported in Table IV are the same properties for 1-methyI-diamantane, 3-methyI-diamantane, and 4-methyI-diamantane as compared with the diamantane data. 

By all accounts, the hypothesis of formation of DNA+adamantane+amino acid nanoarchitectures is currently immature and amenable to many technical modifications. Advancement in this subject requires a challenging combination of state-of-the-art approaches of organic chemistry, biochemistry, proteomics, and surface science. 

Secondary Alkyl Alcohols. Treatment of secondary alkyl alcohols with tri-fluoroacetic acid and organosilicon hydrides results only in the formation of the trifluoroacetate esters no reduction is reported to occur.1,2 Reduction of secondary alkyl alcohols does take place when very strong Lewis acids such as boron trifluoride126 129 or aluminum chloride136,146 are used. For example, treatment of a dichlo-romethane solution of 2-adamantanol and triethy lsilane (1.3 equivalents) with boron trifluoride gas at room temperature for 15 minutes gives upon workup a 98% yield of the hydrocarbon adamantane along with fluorotriethylsilane (Eq. 10).129... 

Of course carbene C-H insertion reactions are well known absolute kinetics have been reported for the insertions of ArCCl into isooctane, cyclohexane, and n-hexane,67 and of PhCCl into Si-H, Sn-H, and C-H bonds.68 More recently, detailed studies have appeared of PhCCl insertions into a variety of substrates bearing tertiary C-H bonds, especially adamantane derivatives.69 Nevertheless, because QMT is considered important in the low temperature solution reactions of MeCCl,60,63 and is almost certainly involved in the cryogenic matrix reactions of benzylchlorocarbene,59 its possible intervention in the low temperature solution reactions of the latter is a real possibility. We are therefore faced with two alternative explanations for the Arrhenius curvature exhibited by benzylchlorocarbene in solution at temperatures < 0°C either other classical reactions (besides 1,2-H shift) become competitive (e.g., solvent insertion, azine formation), or QMT becomes significant.7,59,66... 

The existence of an ion pair stabilized by a solvent molecule in the product-determining step of the reaction has been established by calculations and also supported by the product composition (equation 89). While the formation of the diiodo derivative is characteristic of all the cited solvents, in tetrahydrofuran this iodination takes place with the predominant formation of l-iodomethyl-3-(4-iodobutoxy)adamantane (equation 89). 

Cyloheptatrienylidene carbene is generated when trimethylsilyltropylium tetra-fluonoborate is treated with a stoichiometric excess of tetra-n-butylammonium fluoride in dichloromethane [50], Although the carbene dimerizes readily, it will react with electron-deficient alkenes (see Section 7.3). Tetra-n-butylammonium fluoride in a stoichiometric amount promotes the formation of adamantylidenevinylidene from 2-bromo-2-(trimethylsilylethynyl)adamantane [51 ]. 

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