Mizoroki-Heck Reactions with 4-Phenoldiazonium Salts

Significantly better yields were achieved in Mizoroki-Heck reactions using 4-phenoldiazonium salts instead of their O-alkylated analogues under otherwise identical conditions. We found that a one-flask deacetylation-diazotation-precipitation sequence starting from paracetamol or acetanilides derived thereof provides a convenient access to the required diazonium tetrafluoroborates. The utility of these arylating agents in palladium-catalyzed C-C bond forming reactions was demonstrated for a one-flask-synthesis of the heterocyclic core of the drug aripiprazole. Notably, the diazonium salt formation from an acetanilide could be combined with two Pd-catalyzed steps in a one-flask sequence, without any exchange of solvents or isolation of intermediates.