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 oneflask 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 À C bond forming reactions was demonstrated for a oneflask-synthesis of the heterocyclic core of the drug aripiprazole. Notably, the diazonium salt formation from an acetanilide could be combined with two Pdcatalyzed steps in a one-flask sequence, without any exchange of solvents or isolation of intermediates.

Arene diazonium tetrafluoroborates can be synthesized from aromatic acetamides via a sequence of deacetylation, diazotation and precipitation, induced by anion exchange. The reaction is conducted as a convenient one-flask transformation with consecutive addition of the appropriate reagents. Exchange of solvents or removal of byproducts prior to isolation of the product is not required. The arene diazonium salts are isolated from the reaction mixture by simple filtration. Two complementary protocols are presented, and the utility of the reaction is exemplified for a synthesis of the diarylheptanoid natural product de-O-methyl centrolobine.

Alkynes and phenol diazonium salts undergo a Pd-catalyzed [2+2+1] cyclization reaction to spiro[4,5]decatetraene-7-ones. This structure was confirmed for one example by X-ray single-crystal structure analysis. The reaction is believed to proceed through oxidative addition of the phenol diazonium cation to Pd(0), subsequent insertion of two alkynes, followed by irreversible spirocyclization.

4-Phenol diazonium salts undergo Pd-catalyzed Heck reactions with various styrenes to 4'-hydroxy stilbenes. In almost all cases higher yields and fewer side products were observed, compared to the analogous 4-methoxy benzene diazonium salts. In contrast, the reaction fails completely with 2- and 3-phenol diazonium salts. For these substitution patterns the methoxy-substituted derivatives are superior.

Acetanilides can be deacetylated and diazotized in situ, and subsequently used in Pd-catalyzed coupling reactions without isolation of the diazonium intermediate. Heck reactions, Suzuki crosscoupling reactions, and a Pd-catalyzed [2 + 2 + 1] cycloaddition have been investigated as terminating C À C bond-forming steps of this one-flask sequence. The sequence does not require the exchange of solvents or removal of by-products between the individual steps, but proceeds by addition of reagents and catalysts in due course.