Iodoarenediazonium salts: A new class of aromatic substrates for differential palladium catalyzed reactions

Selectivity studies in the reaction between iodobenzene and phenylacetylene: Sonogashira coupling vs hydroarylation

“…Diazonium salts that are well-recognized as the most reactive substrates for C-C coupling [22] were also tested. However under our conditions, PhN 2 BF 4 failed to afford coupled products even in presence of CuI as co-catalyst, as already observed by Bräse's [23] and Sengupta's [24] groups. As PPh 3 is reported to lower yields in Heck coupling between diazonium salts and olefins, [25] our reactions employing diazonium salts were conducted in the absence of ligands.…”

CC Bond‐Forming Reactions

“…It has been widely employed on a solid phase in various intra- [126,127,128,129] and intermolecular [28,30,127,130,131,132,133,134,135,136,137,138] versions. It is the coupling of an aryl or vinyl chloride [132], bromide [129,132,135,137,138,139], iodide [126,127,128,131,133,134,135,136,139], triflate [130], iodonium salt [30,140], or diazonium salt [29] with an alkene.…”

“…The catalytic cycle is initiated by oxidative addition of an aromatic halide Ar-X' (2) to a stabilized Pd(0) species (1); attack of the acetylide follows. In many reactions, copper acetylides (29), which are generated from the alkyne and CuI in the presence of an amine base, give superior results (Scheme 4).…”

“…In these cases the ligand molecules associate themselves spontaneously with the air-stable Pd salt if co-solvated in an appropriate solvent. Various bases have been used as co-catalysts, among them KOH [43], Na 2 CO 3 [7,15], K 2 CO 3 [8,9,44], KHCO 3 [44], Ba(OH) 2 [29], NEt 3 , CsF [45,46], KF [8], and K 3 PO 4 [6,8,20,21,24]. Unfortunately their impact on the yield of a given coupling and the purity of the final products are difficult to estimate [47].…”

“…Surprisingly, the latter base is even effective in coupling reactions involving a three-phase system with the aryl halide component on a polystyrene support, dioxane as a liquid phase, and the base as second solid phase. Diazonium salts react with arylboronates in alcohol without additional base, but these couplings may follow a different mechanism [26,28,29,48].…”