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

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 p-toluenesulfonic 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 3-phenyl group were occupied by bromine atoms, o-bromination then occurred at the 1-phenyl group with the aid of the olate oxygen.

Automated summary

The Pd-catalyzed bromination of mesoionic 1,3-diphenyltetrazolium-5-olate was developed, with the 4-nitrogen atom acting as a directing group. Specific conditions were used to achieve bromination, demonstrating the role of the palladium catalyst and bromine reagent in the reaction.