Regioselective halo- and carbodesilylation of (trimethylsilyl)-1-methylpyrazoles

Franz Effenberger & Andreas Krebs
The isomeric 3-, 4-, and 5-(trimethylsily1)- as well as the 3,4-, 3,5-, and 4,5-bis(trimethylsilyl)-l-methylpyrazoles (2,7,3,5,9,a nd 10, respectively) are obtained by methylation of the corresponding (trimethylsily1)-1H-pyrazoles or by silylation of Grignard or lithio derivatives of appropriate 1-methylpyrazoles with chlorotrimethylsilane. 5 and 10 are halodesilylated regioselectively by Br2 or ICl in the 4-position, yielding 13 and 15. With additional bromine, these monobromo compounds suffer exclusively bromodesilylation to give 3,4- and 4,5-dibromo-lmethylpyrazole (14 and 16, respectively). These...
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