Electrophilic substitution aryllithium compounds

Summary Using a new synthetic pathway, four intramolecularly donor-stabilized silenes, R(Me3Si)Si=C(SiMe3)2 (10 R = 8-dimethylamino-l-naphthyl 11 R = 2 -(dimethylaminomethyl)phenyl 14 R = 2,6-bis(dimethylaminomethyl)phenyl 15 R = 2,6-bis(diethylaminomethyl)phenyl)), were prepared by the reaction of (dichloromethyl)tris(trimethylsilyl)silane (Ic) with the respective dialkylamino substituted aryllithium compounds (molar ratio 1 2). X-ray structural analyses of the four silenes revealed strong donor-acceptor interactions between the dialkylamino groups and the electrophilic silene silicon atoms, leading to pyramidalization at the silicon centers. The configuration at the silene carbon atoms was found to be planar. The chemical behavior of the new silenes, particularly reactions with water and methanol, treatment with methyl iodide or methyl triflate and conversions with benzaldehyde, are discussed. 

Electrophilic Substitution Reactions in Aryl Grignard and Aryllithium Compounds That Are Accessible from Aryl Halides... 

Electrophilic quench of aryllithium species with carbonyl electrophiles is particularly efficient. However, alkyl halides (other than iodomethane) are poor electrophiles, probably owing to competing elimination reactions (see Section 2.1). The formation of alkyl-substituted aromatic compounds can be achieved, however, by using epoxide electrophiles or by lithiation and reaction of 2-methylbenzamides, themselves generated by orr/ o-lithiation. For example, the benzamide 128 can be deprotonated at the benzylic position and treated with a variety of electrophiles. Addition of aromatic aldehydes gives, after lactonization, 3-aryl-3,4-dihydroisocoumarins (1.119). 

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