Organolithium compounds aromatic nucleophilic substitution

When CH3Li or n-BuLi is used in halogen-metal exchange, a rather electrophilic MeX or n-BuX is obtained as a by-product. The alkyl halide can undergo S 2 substitution with the organolithium compound as nucleophile to give the nucleophilic aromatic substitution product. However, Sn2 reactions of organolithium compounds with alkyl... 

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,... 

Other unconventional methods were also developed for introducing substituents into the phenyl ring of the 5-aryltetrazoles. Reaction of organolithium compounds (BuLi, PhLi, /)-tolyllithium, 1-naphthyllithium, etc.) with 2-cumyl-5-(2-methoxyphenyl)tetrazole 330 (in hexane, 23 °C, 4.5 h) led to corresponding products of nucleophilic aromatic substitution such as 331 and 332 in 47-90% yields <1999JOC9301>. 

Strong nucleophiles such as organolithium or organomagnesium derivatives do not react with substituted or unsubstituted phosphabenzene or arsabenzene (Y = P or As) by nucleophilic substitution as in the case of pyridines, but by addition to the heteroatom forming intermediate anions. These anions can then be converted into non-aromatic compounds by reaction with water yielding 1-alkyl-1,2-dihydro-derivatives, or they can be alkylated by an alkyl halide with the same or a different alkyl group, when two products may result a l,2-dialkyl-l,2-dihydro-derivative, or a 2 -derivative (Figure 17). The former products are kinetically controlled, whereas the latter compounds are thermodynamically controlled. 

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. ... 

---