Synthesis of potassium 4-(1-azol-1-yl)-2,3,5,6-tetrafluorophenyltrifluoroborates from K[C6F5BF3] and alkali metal azol-1-ides. The dramatic distinction in nucleophilicity of alkali metal azol-1-ides and dialkylamides

Abstract

Nucleophilic substitution of fluorine atom in K[C6F5BF3] with alkali metal azol-1-ides in polar aprotic solvent (DMF, DMSO) at 60–130°C gives potassium 4-(azol-1-yl)-2,3,5,6-tetrafluorophenyltrifluoroborates, K[4-AzC6F4BF3] (AzH=pyrrole, pyrazole, imidazole, indole, and benzimidazole). Unexpectedly, diethylamine and morpholine do not react with K[C6F5BF3] under the same conditions while pentafluorobenzene and R2NC6F4H form at 150°C. Reaction of K[C6F5BF3] with Na[NR2] in diglyme or DMSO proceeds similar way. The assumed reason is the relatively low nucleophilicity of both secondary amines and alkali metal dialkylamides which results in destructive by-reaction with K[C6F5BF3] rather than in its aminodefluorination. This is confirmed by the competitive nucleophilic aminodefluorination of a model substrate, C6F5Ph, with sodium indolide/sodium morpholinide.