Adamantyl radicals, reactivity

By competition experiments the Ph2P ion is 830 times more reactive than the PhS ion toward the 1-adamantyl radical in DMSO, but only 8.4 times more reactive toward thep-anisyl radical. This reactivity difference was attributed to the greater stability of the 1-adamantyl radical compared with the / -anisyl radical123. 

Relative reactivity studies of homolytic substitution of monosubstituted benzene derivatives reveal that the 1-adamantyl radical has more pronounced nucleophilic properties than have other, more strained, bridgehead radicals. With benzo-nitrile 21.1) almost exclusive para-substitution is observed, whereas with anisole 0.65) the three possible sites are attacked almost equally. Kinetic studies on the reaction of adamantanethione with adamantane-2-thiol indicate that the rate-controlling chain-propagation step is hydrogen abstraction from the thiol (AdHSH) by the carbon-centred radical AdHSSAd-, and that the main mode of termination involves the diffusion-controlled bimolecular self-reaction of these radicals. ... 

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. ... 

Adamantyl sulfides 576 have been prepared by radical decarboxylation of [bis(l-adamantane-carboxy)iodo]benzene 575 (Ar = Ph) in the presence of disulfides 574 (Scheme 3.227). A study of the reactivity of various [bis(l-adamantanecarboxy)iodo]arenes 575 in this reaction has shown that the introduction of strong electron-withdrawing groups, such as nitro and perfluoro, into the aromatic ring of 575 leads to a significant reduction of the yield of product 576, which is explained by the lower reactivity of p-nitro and perfluorophenyl derivatives 575 in radical reactions due to the increased I—O bond strength in these compounds [619]. 

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