Palladium-catalyzed oxyarylation of olefins using silver carbonate as the base. Probing the mechanism by electrospray ionization mass spectrometry

The Pd(OAc)2-catalyzed oxyarylation of electron-rich (8 and 12) and electron-poor (10) olefins by ortho-iodophenols (3a–d) was studied using Ag2CO3 as the base, in acetone, and in the presence and absence of PPh3. The corresponding adducts of oxyarylation were obtained in moderate yields. The reaction mechanism was examined by electrospray ionization mass spectrometry (ESI-MS). Cationic arylpalladium intermediate (14), formed by the oxidative insertion of Pd(0) into 3a, and the cationic palladacycles (15), obtained by reaction of 14 with olefins 8 and 12, were intercepted by ESI-MS and characterized by ESI-MS/MS.

The mechanism of the Pd-catalyzed oxyarylation of 8 by 3a leading to (±)-9a was investigated by electrospray ionization mass spectrometry. The key intermediate cyclo-palladate 15b was intercepted and characterized. The scope of this synthetically useful reaction was studied using other olefins (10 and 12) and ortho-iodophenols (3b,c,d). A similar cationic intermediate was intercepted in the reaction of 12 with 3a. Competitive experiments show that reactivity order toward 3a is 8 > 12 > 10.Figure optionsDownload as PowerPoint slide