Synthesis of 1,4-dimethyl(phenyl)silyl- and triphenylsilyl-3-tert-butyl-8-methylpyrazolo[5,1-c][1,2,4]triazines

Abstract

Reactions of 3-tert-butyl-8-methylpyrazolo[5,1-c][1,2,4]triazine with lithium phenyldimethylsilanide and triphenylsilanide in THF media at −85 to −60 °C led to the formation of the silicon C(4)-addition products in high yields. Aromatic 3-tert-butyl-8-methyl-4-(triphenylsilyl)pyrazolo[5,1-c][1,2,4]triazine has been synthesized by oxidation of the corresponding 1,4-dihydro derivative using NBS/Et3N in pentane at −30 to −15 °C. Preferential N(1)-nucleophilic additions of silanides were observed for the sterically hindered 3,4-di-R-8-methylpyrazolo[5,1-c][1,2,4]triazines (R = t-Bu, Ph3Si). Novel C–Si derivatives of 1,2,4-triazines, as well as some other isolated compounds were characterized by IR, 1H, 13C, 29Si NMR, HRMS data and X-ray crystallography.