Triarylmethyl radicals, preparation

The diketone 64 was also readily prepared from 59 as outlined in Scheme 20.15. Condensation between 64 and 2 equiv. of 51b gave 65 in excellent yield. Thermolysis of 65 in 1,4-CHD at 75 °C also promoted the Myers-Saito cyclization reaction to generate the biradical 66. The aryl radical center in 66 was then captured by the allenic moiety to form 67, having two stabilized triarylmethyl radical centers. Subsequent hydrogen-atom abstractions from 1,4-CHD then furnished 68. 

The basic significance of Gomberg s work remains unchanged. Many dimers have been prepared, and the existence of free triarylmethyl radicals has been substantiated in a number of ways indeed, certain of these compounds seem to exist entirely as the free radical even in the solid state. The most convincing evidence for the free-radical nature of these substances lies in properties that arise directly from the odd electron that characterizes a free radical. Two electrons... 

The same thing happens when alkyl halides are treated with silver in the presence of oxygen.41 The reaction with silver in the absence of oxygen is of course one of the methods used to prepare the stable triarylmethyl free radicals. 

Both the results and the reasoning, however, were rigorously confirmed shortly thereafter. Eventually it became clear that Gomberg s synthetic failure led to the discovery of stable radicals, a new class of organic species, derivatives of trivalent carbon. Further studies led to the understanding that the triarylmethyl system is extremely versatile and gives rise to the preparation of other types of derivatives of trivalent carbon, e.g. salts of the triphenylmethyl cation 66b and the triphenylmethyl anion 66c. 

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