Preparation of 1-hydroxypyrazoles and 1-hydroxy-1,2,3-triazoles by dealkylation of pyrazole and triazole N-oxides

Abstract

1-Hydroxypyrazoles were obtained from 2-benzylpyrazole 1-oxides by debenzylation with iodotrimethylsilane. 1-Hydroxy-1,2,3-triazoles were achieved from 2-benzyltriazole 1-oxides by debenzylation effected with conc. hydrobromic acid or from 2- or 3-p-methoxybenzyltriazole 1-oxides by de-p methoxybenzylation accomplished by treatment with conc. sulfuric acid. 1-Methoxy-1,2,3-triazole was obtained by de-p-methoxybenzylation of 1-methoxy-3-p-methoxybenzyl-1,2,3-triazolium tetrafluoroborate accomplished by treatment with conc. sulfuric acid. 1-Hydroxypyrazole was selectively N-benzylated in absence of base to give 2-benzylpyrazole 1-oxide which, upon selective substitution at the 3-position and subsequent debenzylation, produced 3-substituted 1-hydroxypyrazole. © Acta Chemika Scandinavica 1996.