Ambident nucleophiles aromatic rings

Palladium(0)-catalyzed allylation of nucleophiles (the Tsuji-Trost reaction) is a versatile synthetic method that has gained immense popularity in recent years. Rarely applied to ambident nucleophilic aromatic heterocycles before 1991, the Tsuji-Trost reaction has been extensively used in the chemistry of these compounds since 1991. Two factors have played decisive roles in this increased interest in the Pd(0)-catalyzed allylation of such heterocyclic rings one is that, unlike other alkylation procedures, the Pd(0)-catalyzed allylation can sometimes give the product of thermodynamic control when applied to ambident nucleophiles and the second is that the Tsuji-Trost allylation has become one of the standard methods for synthesizing carbanucleosides, which are important antiviral compounds (93MI1, 93MI2). Of course, the double bond of an allylic system can be modified in different directions, thus adding versatility to the Tsuji-Trost reaction. 

The associative step (equation 3) determines the nature of the product, since in this step the synthetically important bond formation between the aromatic moiety and the nucleophile takes place. The rates for the association of a number of nucleophiles with a variety of aryl and heteroaryl radicals has been measured in electrochemical studies29-31 and competitive product studies.32-35 The range of nucleophiles, classified according to the atom which becomes directly bonded to the aromatic ring, and, where the nucleophile is ambident, the regiochemistry of the association reaction shown in equation (3) are detailed in Section 2.2.3. The final propagating step (equation 4), that returns the chain-propagating electron from product radical anion to another molecule of substrate, is essential if a chain reaction is to continue. 

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