Palladium‐Catalyzed Selective o‐Bromination of Mesoionic 1,3‐Diphenyltetrazolium‐5‐olate: Switching the Directing Group from Nitrogen to Oxygen

Abstract

Pd-catalyzed bromination of mesoionic 1,3-diphenyltetrazolium-5-olate (1) was developed. In the presence of palladium acetate (5 mol%), N-bromosuccinimide (110 mol%), and ptoluenesulfonic acid (50 mol%) in 1,2-dichloroethane under reflux, olate 1 underwent bromination to give 1-(2-bromophenyl)-3-phenyltetrazolium-5-olate in a moderate yield as the major product, indicating that the 4-nitrogen atom acts as a directing group rather than the negatively charged oxygen atom. The X-ray-suitable crystals of the corresponding palladacycle were isolated from 1-mesityl-3-phentytetrazolium-5-olate and fully characterized. When both the o-positions of the 3phenyl group were occupied by bromine atoms, o-bromination then occurred at the 1-phenyl group with the aid of the olate oxygen.

A Practical Method for the Synthesis of Mesoionic 1,3-Diaryltetrazolium Derivatives Bearing a para-Substituted Phenyl Group at the 1- or 3-Position from Anilines

“…In the synthesis of 1,3-diphenyltetrazolium compounds, phenyl isothiocyanate and phenylhydrazine are used, and two phenyl groups derived from the two phenyl compounds are respectively introduced on the tetrazolium ring (Scheme 1 ). Therefore, 1,3-diaryltetrazolium compounds bearing a substituent on the phenyl group require substituted aryl isothiocyanates (for modification of the phenyl group at the 1-position) or arylhydrazines (for modification of the phenyl group at the 3-position) as building blocks; 4b however, in contrast to unsubstituted materials, commercially available reagents are limited or expensive.…”