1-Adamantyl radical

Star polymers are a class of polymers with interesting rheological and physical properties. The tetra-functionalized adamantane cores (adamantyls) have been employed as initiators in the atom transfer radical polymerization (ATRP) method applied to styrene and various acrylate monomers (see Fig. 21). 

Figure 21. Atom transfer radical polymerization (ATRP) synthetic route to tetrafunctional initiators of a star polymer with adamantyl (adamantane core). Taken from Ref. [91] with permission.

Figure 9.32. Electron transfer in the adamantane radical cation (bis (methylene) adamantyl radical cation).

Computational study at 6-31 lg level of theory of l-bora-4-adamantyl radicals showed that ry -isomer 14a is more stable than anti-one 14b by 0.23 kcal mol-1 (Figure 3). These radicals are proposed <1999CRV1377> to be the intermediates in reduction of 4- A-chloro-l-boraadamantane with -Bu3SnD <1996JOC9588>. 

The interaction between two adjacent bulky groups can depend on steric factors which are not necessarily related to the stability of the radicals produced on homolysis. It is estimated from linear free energy relationships that only 65-70% of the ground-state strain energy is relieved in the transition state for homolysis of a bond between two quaternary centres (Ruchardt and Beckhaus, 1980, 1986). Thus steric constraints to delocalization in the radicals produced may persist. A pertinent example is 2,3-di(l-adamantyl)-2,3-dimethylbutane [123] which has four such centres, linked by the long C-C bonds characteristic of this sort of structure. The strongest... 

Hindered di-t-alkylamines RNHBu1 (R = t-Bu, t-octyl or 1-adamantyl) have been synthesized from t-alkylamines as follows. Reaction with peracetic acid gave the nitrosoalkanes RNO, which were treated with t-butyl radicals, generated from t-butylhydrazine and lead(IV) oxide, to yield t-butyloxyhydroxylamines. Reduction with sodium naphthalide in THF gave the products (equation 12). The di-t-alkyl-amines are inert to methyl iodide and dimethyl sulphate but can be alkylated by methyl fluorosulphonate42. 

The competition between ET and 5n2 processes in the reaction between radical anions of various aromatic compounds, e.g. anthracene, pyrene, (E)-stilbene, and m- and / -cyanotoluene, and substrates such as RHal (where R = Me, Et, Bu, 2-Bu, neopentyl, and 1-adamantyl) or various methanesulfonates has been studied in DMF as solvent. The reaction mechanism could be characterized electrochemically in many of the systems indicated above. The presence of an 5n2 component is related not only to the steric requirements of the substrate, but also to the magnitude of the driving force for the ET process. 

Dinitrogen pentoxide reacts with alkanes in carbon tetrachloride at 0 °C via a radical mechanism to give nitration products which can include nitrate esters.Reactions of alkanes with dinitrogen pentoxide in nitric acid are complex and of little synthetic value. 1-Adamantyl nitrate is one of the products obtained from the photochemical irradiation of a solution of adamantane and dinitrogen pentoxide in methylene chloride. ... 

Azoadamantane exposed to 2 mol equivalents of T CIO4 at room temperature rapidly and quantitatively evolved nitrogen, and thianthrene and products derived from the adamantyl cation were obtained. Equations (38)-(40) (AA, azo-adamantane Ad, adamantane) make clear why 2 mol equivalents of the radical oxidant are required (85JA2561). The comparable interaction of T with phenylazotriphenylmethane and di-ter/-butyl diazene, using a 2 1 ratio of radical cation to substrate, also leads to the formation of thianthrene and nitrogen (85PS111). 

Tris[(2-perfluorohexyl)ethyl]tin hydride has three perfluorinated segments with ethylene spacers and it partitions primarily (> 98%) into the fluorous phase in a liquid-liquid extraction. This feature not only facilitates the purification of the product from the tin residue but also recovers toxic tin residue for further reuse. Stoichiometric reductive radical reactions with the fluorous tin hydride 3 have been previously reported and a catalytic procedure is also well established. The reduction of adamantyl bromide in BTF (benzotrifluoride) " using 1.2 equiv of the fluorous tin hydride and a catalytic amount of azobisisobutyronitrile (AIBN) was complete in 3 hr (Scheme 1). After the simple liquid-liquid extraction, adamantane was obtained in 90% yield in the organic layer and the fluorous tin bromide was separated from the fluorous phase. The recovered fluorous tin bromide was reduced and reused to give the same results. Phenylselenides, tertiary nitro compounds, and xanthates were also successfully reduced by the fluorous fin hydride. Standard radical additions and cyclizations can also be conducted as shown by the examples in Scheme 1. Hydrostannation reactions are also possible, and these are useful in the techniques of fluorous phase switching. Carbonylations are also possible. Rate constants for the reaction of the fluorous tin hydride with primary radicals and acyl radicals have been measured it is marginally more reactive than tributlytin hydrides. ... 

Isoquinoline has been alkylated with tertiary halides such as terf-butyl40 or adamantyl halides.41 Isoquinoline is reduced more easily than the halides and the mechanism is believed to involve alkyl radicals formed by homogeneous electron transfer from the heteroaromatic anion-radical A. ... 

Ipso attack has been detected at both a-positions in the reaction of methyl and adamantyl radicals with methyl 5-nitrofuran-2-carboxylate and 5-nitrofuran-2-carbaldehyde. A typical example is shown in Scheme 43. Ipso attack at the carbon bearing the nitro group leads to substitution via the [Pg.617]

Two situations are conducive to ipso attack. If polar effects come into play in stabilizing the transition state of the addition of the radical, then frequently ipso attack is encountered. This is clearly brought out in the different behaviour of adamantyl and methyl radicals towards the same substrate. It has been firmly established that while methyl and phenyl radicals are electroneutral, the bridgehead adamantyl radical behaves as a nucleophilic species (80ACR51). If this adamantyl radical is reacted with thiophene substrates made electron deficient by the presence of suitable substituents, then the transition state of the addition step may have the character of a charge-transfer complex the site at which the... 

It is obvious from the examples of ipso substitution discussed above that the elimination of N02 from the ipso intermediate is greatly favoured [k2 k ), leading irreversibly to the substitution products. This is because -N02 is a stable radical. On the other hand, if in the ipso intermediate (229) both R and X form strong bonds to the carbon atom, then the intermediate may be forced to decay by other processes, i.e. neither revert to (228) nor undergo substitution to (230). An example is provided by the reaction of the dialdehyde (239) with the adamantyl radical (Scheme 65) (80ACR51, 80JCS(P2)1336). The two major products are 2-adamantylthiophene-5-carbaldehyde (241 19%) and 2-adamantyI-thiophene-3,5-dicarbaldehyde (244 56%). The formation of both can be explained from the common ipso intermediate (240). The loss of the formyl group from this to form (241)... 

One interesting feature of anion radical photochemical behavior has been described recently by Camps et al. (2001). The anion radical of bromoadamantane loses bromide and gives the adamantyl radical. This photoactivated radical undergoes 1,5-hydrogen shift. Reactions of such kinds were not observed before. 

Similar internal cyclizations occur when 2- (l-adamantyl)-ethanol is treated with lead tetraacetate to give the cyclic ether 83 217 >283 or with HOC1 to give 84 (Eq. (70)) 2831. These reactions apparently involve hydrogen abstractions by the initially formed alkoxy radical. 

Comparison of the cyclic systems in Table 17 leads to the opposite conclusion, however the destabilization of the 1-norbornyl radical relative to the 1-adamantyl is less for the azo decompositions. Perhaps the mechanism of the azo decompositions of the more unreactive systems is different from that of, for example, the f-butyl azo compound (i.e. the rate determining step of the 1-norbomyl azo compound may be a one bond homolysis rather than the synchronous two bond fission of the f-butyl system312, 315)). Also, the smaller 1-norbornyl/1-adamantyl rate ratio for the f-butyl perester decompositions may be due to a greater influence of polar effects in these reactions 309a). This problem is under active investigation 309a). 

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