Silylation of azole N-oxides

Abstract

Pyrazole N-oxides and 1,2,3-triazole N-oxides can be C-silylated at ring and exocyclic α-positions in high yields in a one-pot procedure by treatment with trimethylsilyl triflate, trimethylsilyl iodide or tert-butyldimethylsilyl triflate in the presence of 1,2, 2,6,6-pentamethylpiperidine, diisopropylethylamine or lithium tetramethylpiperidide. The reaction is initiated by O-silylation, followed by deprotonation of ring or exocyclic α-positions, and terminated by silylation of the generated anion. The activating O-silyl group is removed by hydrolysis.

Immonium ring carbon atoms are more reactive than enammonium ring carbon atoms. Silylation of exocyclic α-positions at enammonium ring carbon atoms require forcing conditions and give modest yields.