Adamantyl derivatives radical reactions

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]. 

Substituted adamantanes have been employed in the study of several reaction mechanisms. The Kolbe electrolyses of 1- and 2-adamantane carboxylic acids and 1- and 2-adamantyl acetic acids have been compared in detail. Car-bonium ion-derived products are observed from the electrolyses of both 1-adamantyl carboxylic acid and 1-adamantyl acetic acid. A mixture of radical and carbonium ion-derived products are obtained from 2-adamantyl carboxylic acid and mainly radical-derived products are obtained from 2-adamantyl acetic acid. These results parallel the known or expected stabilities of the intermediate carbonium ions 366 ... 

Pyridine is attacked by the adamantyl radical to give a mixture of C-2 and C-4 isomers (Equation 104) <1995ZOR670>. The analogous reaction of ethyl isonicotinate gave mainly the 2-substituted derivative. 

Alkyldenitration by the 1-adamantyl radical in / ara-substituted nitrobenzenes (/7-X-C6H4-NO2) is an efficient process only for electron-poor arenes. Thus, while for anisole (X = OMe), benzene (X = H) and toluene (X = Me) derivatives no ipso products were observed, the analogous reaction with nitrobenzenes bearing electron withdrawing substituents (X = NO2, CN, SO2R, CO2R, COMe, CHO) afforded the corresponding alkyldenitration products in 45-60 /) yield [30]. The effect of the... 

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. ... 

Most of the substrates discussed before feature sp or sp -hybridized carbon atoms connected to the leaving groups. However, there are some reports indicating that some sp -hybridized substrates undergo Heck-type reactions. At least in some cases, radicals or cationic species are involved. For example, 1-bromoadamantane derivatives react with alkenes under palladium catalysis to give rise to 1-adamantyl alkenes (Scheme 5-39) (Experimental Procedure below). 

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