Adamantane alkylation with

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... 

Superacid-catalyzed alkylation of adamantane with lower alkenes (ethene, propene, isomeric butenes) has been investigated by Olah et al.151 in triflic acid and triflic acid-B(0S02CF3)3. Only trace amounts of 1 -ferf-butyladamantane (37) were detected in alkylation with 1- and 2-butenes, whereas isobutylene gave consistently relatively good yield of 37. Since isomerization of isomeric 1-butyladamantane under identical conditions did not give even traces of 37, its formation can be accounted for by (r-alkylation, that is, through the insertion of the ferf-butyl cation into the C—H bond (Scheme 5.22). This reaction is similar to that between ferf-butyl cation and isobutane to form 2,2,3,3-tetramethylbutane discussed above (Scheme 5.21). In either case, the pentacoordinate carbocation intermedate, which may also lead to hydride transfer, does not attain a linear geometry, despite the unfavorable steric interactions. 

The methylations of l,3-dilithio-5,7-dimethyl-2,4,6,8-adamantane and of 1,3,5,7-tetrathiacyclooc-tane tetraanion- are of theoretical value only. 1,3,5-Trithiane and both mono- and 2,4,6-trialkyl-substituted derivatives have been metallated - with n-butyllithium and alkylated - with reactive alkylating agents such as primary alkyl iodides or bromides and benzyl bromide (Scheme 73, entries a and b). The metallation of monoalkylated trithianes occurs at one of the two unsubstituted sites and leads eventually to the product having both substituents in the equatorial position. - Thus the high equatorial preference for lithium in 2-lithio-l,3-dithiane is also present in 2-lithio-2-methyl-l,3,5-trithiane. Mer-... 

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]... 

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

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... 

Pioneering work on the desulphonylation of jS-ketosulphones was carried out by Corey and Chaykovsky - . This reaction was part of a sequence which could be used in the synthesis of ketones, as shown in equation (53). The main thrust of this work was in the use of sulphoxides, but Corey did stress the merits of both sulphones and sulphonamides for different applications of this type of reaction. The method soon found application by Stetter and Hesse for the synthesis of 3-methyl-2,4-dioxa-adamantane , and by House and Larson in an ingenious synthesis of intermediates directed towards the gibberellin skeleton, and also for more standard applications . Other applications of the method have also been madealthough it does suffer from certain limitations in that further alkylation of an a-alkyl- -ketosulphone is a very sluggish, inefficient process. Kurth and O Brien have proposed an alternative, one-pot sequence of reactions (equation 54), carried out at — 78 to — 50°, with yields better than 50%. The major difference between the two routes is that the one-pot process uses the desulphonylation step to generate the enolate anion, whereas in the Corey-House procedure, the desulphonylation with aluminium amalgam is a separate, non-productive step. 

Bromoadamantane and 1-bromoadamantane are reduced to adamantane in yields of 84% and 79%, respectively, when treated with triethylsilane and catalytic amounts of aluminum chloride.186 Similar treatment of benzhydryl chloride and exo-2-bromonorbomane gives the related hydrocarbons in yields of 100% and 96%, respectively.186 In contrast, 2-bromo-l-phenylpropane gives only a 43% yield of 1-phenylpropane the remainder consists of Friedel-Crafts alkylation products.186 Some alkyl halides resist reduction by this method, even when forcing conditions are employed. These include p-nitrobenzyl bromide, 3-bromopropanenitrile, and 5-bromopentanenitrile.186... 

Oxygen-centered phosphanides are accessible by hydrolysis of the phospha-nides as shown for the oxygen-centered phosphanide 73 of the formula [Sr40- P(SiMe2Prl)2 6] with an Sr4P6 adamantane-like structure as shown in Eq. (7) [74], The strontium atoms are coordinatively saturated by agostic interactions to the silicon-bonded alkyl substituents. 

Insertion occurs at the respective a-position of the alkyl substituent. Using a 3 1 ratio of CHBr, to substrate. With a trace of l-(2,2-dichloroethoxy)adamantane.d 1- and 4-isomers in a 1.7 1 ratio. + 2,5-bis(dichloromethyl) derivatives (40%). > Insertion into the tertiary CH. 

Tricyclic molecules having 10 carbon atoms are converted to adamantane with Lewis acids. Additional carbon atoms become alkyl appendages ... 

The reaction of adamantane with lower alkenes (ethylene, propylene, and butylenes) in the presence of superacids [CF3SO3H or CF3SO3H—B(0S02CF3)3] shows the involvement of both alkylations.34 In the predominant reaction the 1-adamantyl cation formed through protolytic C—H bond ionization of adamantane adamanty-... 

This process is called direct a alkylation. Even the formation of ferf-butyladaman-tane was observed in the superacid-catalyzed alkylation of adamantane with isobutylene necessitating a highly crowded, unfavorable tertiary-tertiary interaction. This provides further evidence for the a-alkylation reaction, as adamantylation of isobutylene with any subsequent isomerization does not lead to this isomer. 

Early structural information about the simple alkyl radicals was obtained by Herzberg, who observed the ultraviolet spectra of CH3 and CD3 in the gas phase by flash photolysis.9 Analysis of the fine structure led to the conclusion that the methyl radical is planar, a deviation from planarity of not more than 10° being consistent with the data.10 The infrared spectrum of GH3 has also been recorded it does not yield conclusive structural information.11 Radicals trapped in a matrix of solid adamantane can be formed by X-irradiation of suitable precursors. In this way, spectra can be obtained at room temperature.12... 

The AcBr-2AlX3 (X = Cl, Br) complexes display high activity in the alkylation of adamantane with alkanes to form poly alkylated adamantanes (Cn < C < C33) and bisadamantylalkanes (C23 < C < C50)119 [Eq. (5.70)]. The suggested pathway includes the 1-adamantyl cation and alkyl cations generated by hydride removal by the superacidic complexes. The 1-adamantyl cation then alkylates alkenes equilibrating with the alkyl cations. Various transformations may follow, resulting in the formation of additional products. 

Laali et al.234 have developed a method to the highly selective pura-adamantylation of arenes (toluene, ethylbenzene, anisole) with haloadamantanes (1-chloro- and 1-bromoadamantane, l-bromo-3,5,7-trimethyladamantane) and 1-adamantanol promoted by triflic acid in butylmethylimidazolium triflate [BMIM][OTf] ionic liquid. In contrast to reactions mn in 1,2-dichloroethane, little or no adamantane byproduct was detected in [BMIM][OTf. Furthermore, no isomerization of para-tolyladamantane was observed supporting the intramolecular nature of the formation of meta isomers. In competitive experiments with benzene-toluene mixture (1 1 molar ratio), high substrate selectivities were found (kT/kB = 16-17) irrespective of the alkylating agent. This is in sharp contrast to values about unity measured in 1,2-dichloroethane. 

Nitrile oxides react with the methyl enol ethers of (Rs)-l -fluoro-alkyl-2-(p-tolylsulfinyl)ethanones to produce (45,5/f,/fs)-4,5-dihydroisoxazoles with high regio-and diastereo-selectivity.87 In the 1,3-dipolar cycloaddition of benzonitrile oxide with adamantane-2-thiones and 2-methyleneadamantanes, the favoured approach is syn, as predicted by the Cieplak s transition-state hyperconjugation model.88 The 1,3-dipolar cycloaddition reaction of acetonitrile oxide with bicyclo[2.2.l]hepta-2,5-diene yields two 1 1 adducts and four of six possible 2 1 adducts.89 Moderate catalytic efficiency, ligand acceleration effect, and concentration effect have been observed in the magnesium ion-mediated 1,3-dipolar cycloadditions of stable mesitonitrile oxide to allylic alcohols.90 The cycloaddition reactions of acryloyl derivatives of the Rebek imide benzoxazole with nitrile oxides are very stereoselective but show reaction rates and regioselectivities comparable to simple achiral models.91. 

Reversible, random carbonium ion formation is not required to explain the rearrangements of both 2 and 37 to adamantane in the highly acidic media. Sequential 1,2 alkyl shifts coupled with the well documented 5316,2- and 3,2-hydride shifts of the norbomyl system permit a rearrangement pathway analogous to that discussed earlier as the most likely route for the Lewis acid catalyzed rearrangement of 2 to adamantane. 

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