Giese-type reaction

Here the reactants can combine to form the ground state of the supposed intermediate. Since the ionization potentials of N (14.54 e.v.) and NO (9.25 e.v.) are very different, any resonance force of the type suggested by Giese (8) will be repulsive but weak. Thus, there should be no barrier to reaction (7), and it is known to be fast at low ion energies (23). 

In the past few years, however, very efficient new methods of cyclisation proceeding via radical intermediates have been developed and several reviews [19a] and a comprehensive book by Giese [19b] have been published. Rather than reactions involving the dimerisation of two radicals -as in the Kolbe electrochemical synthesis [20] or the radical induced dehydrodimerisation developed by Viehe [21]-more important are the reactions between a radical with a non-radical species. The advantage of this type of reaction is that the radical character is not destroyed during the reaction and a chain-reaction may be induced by working with catalytic amounts of a radical initiator. However, in order to be successful two conditions must be met i) The selectivities of the radicals involved in the chain-reaction must differ from each other, and ii) the reaction between radicals and non-radicals must be faster than radical combination reactions. 

The combination of the catalytic method and the three-phase separation could be applied to the parallel rapid synthesis of a small library of nine compounds of type 7 using the Giese reaction (eq. 5.3). The attractive prospect from this simple experiment arises from the very efficient workup protocol, allowing facile and quantitative separation even if excess reagents... 

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