Organolithium reagents aromatic nucleophilic substitution

Apart from nucleophilic substitution reactions, the chemistry of the halo derivatives of the 7r-deficient heterocycles is fairly similar to that of aromatic halides. Thus, heterobiaryls can be prepared by the Ullman reaction, and Grignard reagents and organolithium compounds can be prepared, although in many instances, and especially with Grignard reagents,... 

Arylchromium complex 733 reacts with carbon nucleophiles via nucleophilic aromatic substitution. As shown in Table 8.29,6 3 organolithium reagents and enolates add to 733 to generate a carbanionic complex... 

Table 8.29. Nucleophilic Aromatic Substitution of 733 by Organolithium Reagents and Enolate Anions...

Tomioka documented the use of organolithium reagents in enantioselec-tive conjugate additions to conjugated imines (Equation 31) [136]. The readily available chiral diether 173 served to mediate such additions with high asymmetric induction for example, the addition of PhLi to 172 furnished aldehyde 174 in 94% ee after hydrolysis of the imine adduct. In subsequent developments, Tomioka reported the enantioselective preparation of biaryls in which a naphthyllithium participates in a nucleophilic aromatic substitution catalyzed by only 5mol% of 173 (see insert on the left) and delivers the product in 82% ee [137]. 

Because the reactions of related in -cyclohexadienyl complexes are synthetically valuable, the reactions of this ligand have been studied extensively. An outline of how this chemistry can be conducted on the Fe(CO)j fragment is shown in Equation 11.51. A variety of cyclohexadienes are readily available from Birch reduction of substituted aromatics. Coordination and abstraction of a hydride, typically by trityl cation, leads to cationic cyclohexadienyl complexes. These cyclohexadienyl complexes are reactive toward organolithium, -copper, -cadmium, and -zinc reagents, ketone enolates, nitroal-kyl anions, amines, phthalimide, and even nucleophilic aromatic compounds such as indole and trimethoxybenzene. Attack occurs exclusively from the face opposite the metal, and exclusively at a terminal position of the dienyl system. This combination of hydride abstraction and nucleophilic addition has been repeated to generate cyclohexa-diene complexes containing two cis vicinal substituents. The free cyclohexadiene is ttien released from the metal by oxidation with amine oxides. ... 

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