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Palladium(II)-catalyzed procedures often use benzoquinone (BQ) to regenerate the catalyst. Besides its oxidation role, BQ can also promote various steps of the catalytic cycle. This review highlights the multifaceted properties of BQ and its analogues when involved in PdII-catalyzed oxidative reactions and presents mechanisms proposed in the literature, in some cases with personal observations. [ABSTRACT FROM AUTHOR]

4,5-Diazafluorenone was found to promote the dehydrogenative Heck reaction of furans and thiophenes with hindered alkenes. High stereoselectivity was achieved in the synthesis of β,β-diaryl α,β-unsaturated alkenes. A mechanism, based on ESI-MS studies, kinetic experiments, and competitive reactions, was proposed. The ligand influences C-H bond activation, insertion of the alkenes, the stereodetermining step, and the aerobic regeneration of the catalyst. [ABSTRACT FROM AUTHOR]

The aerobic dehydrogenative Heck reaction (DHR) of heterocycles with styrenes was found to be more efficient in the absence of metallic co-oxidants. According to a study of the isotope effect, the CH cleavage was the rate-determining step of the catalytic cycle. Electrospray ionization mass spectrometry, subsequent MS/MS, and high-resolution mass spectrometry were used to detect and characterize catalytic intermediates and species formed in the presence of metallic co-oxidants. [ABSTRACT FROM AUTHOR]