Ring Metallation and Reactions of C-Metallated Derivatives

Benzothiazoles and benzimidazoles (blocked or protected on nitrogen) lithiate at the hetero-ring 2-position. This allows subsequent reaction with the usual range of electrophiles the examples below show the introduction of iodine and a silicon substituent 2-lithio-benzimidazoles also react efficiently with simple esters to give ketones.  

Lithiation of benzoxazole leads to a mixture of the 2-lithiated species and a ring-opened ortfto-isocyano-phenolate. This difficulty can be avoided by magnesation and good yields of 2-substituted products obtained thereby.  

Lithiation of 2-alkyl-2/f-indazoles proceeds straightforwardly and thus 3-substituted 2/f-indazoles can be obtained and comparable lithiations of 2-trimethylsilyl-indazoles, followed by removal of the silicon substituent, produce 3-substituted indazoles. 

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