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.