Carbodesilylierung von (Trimethylsilyl)imidazolen und ‐pyrazolen

Carbodesilylation of (Trimethylsilyl)imidazoles and ‐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.