ELECTROPHILIC AROMATIC SUBSTITUTION .37. CARBODESILYLATION OF (TRIMETHYLSILYL)IMIDAZOLES AND (TRIMETHYLSILYL)PYRAZOLES

The preparation of the 1-methyl(trimethylsilyl) (TMS)-substituted imidazoles 3a, 4a, 8, 9, and 11a by silylation of the corresponding metallated imidazoles is described. Carbodesilylation of 3 with aldehydes or carboxylic halogenides occurs selectively in 2-position. In the presence of a strong base (CsF) the reactivity against carbon electrophiles correlates well with the stability of the imidazolyl anions; regioselective carbodesilylation in 2-, 5-, or 4-position of the twofold TMS-substituted imidazoles 3a and 9 therefore is possible, which allows the synthesis of a great variety of hydroxyalkyl-substituted imidazoles and of acylimidazoles. By using the dimethylsulfamoyl substituent as an N-protecting group, the N-unsubstituted 5-benzoylimidazole (26) as well as the comparable 5-benzoyl-pyrazole (30b) and 5-(hydroxyphenylmethyl)-pyrazole (30a) are accessible.