Synthesis of Chlorinated Biphenyls by Suzuki Cross‐Coupling Using Diamine or Diimine‐Palladium Complexes

Abstract

Several novel diimines (Salen-type ligands) 2a-2i and their reduced diamine counterparts 3b,3d-3g and 3i form complexes 4a-4i, 5b,5d-5g, and 5i with PdCl 2 in DMF or methanol. Using 1 mol-% of the isolated complexes 4e and 5f many polychlorinated biphenyls (PCBs) can be prepared in moderate to excellent yields according to the Suzuki crosscoupling protocol with contact to air. Several 4-acetylbiphen-

One step synthesis of Diflunisal using a Pd-diamine complex

“…PdCl 2 without being complexed The reaction proceeded under air and yielded highly pure crystalline Diflunisal after very simple purification on a slilica column to remove the palladium catalyst. The palladium-diimine complex (8) was also examined in the Suzuki reaction because of its demonstrated catalytic abilities in PCB syntheses [14]. However, in the case of Diflunisal synthesis, the reaction proceeded in low yield ( Although the reactions had to be performed at higher temperatures, the advantage was to obtain the products in higher purity.…”

“…Transition metal catalyzed cross-coupling reactions are efficient methods to prepare the carbon-carbon bond found in biaryls [13][14][15][16]. For example Suzuki coupling reactions provide a general approach to arylaryl C-C bond formation [17,18].…”

“…Development of efficient phosphine free catalysts for preparation of hydrophilic substrates are of interest and reactions without a phosphine ligand, strong base and free hydroxyl groups in arylhalide have been reported recently [43,44]. As part of our ongoing projects considering synthesis of biphenyl carboxylic acids and low-molecural sized drugs employing Pd-catalysts [5,14,27,45], we have noticed that Pd/C has turned out to be a good catalyst for arylation of bromobenzoic acids [27]. Pd/C is also reported to catalyze reactions of halophenols, though in these reactions iodine is required as the halide and/or the use of microwave power for effective reactions [46,47].…”

“…2) were prepared as previously reported [14]. Pd/C (5%) was purchased from Sigma-Aldrich and used as water wet 50% without purification.…”

“…We have recently noticed that 3 eq K 2 CO 3 is the optimal amount of base to be employed in Suzuki reactions when using catalysts 6-8 [14]. Therefore, 4 or 5 eq of base, depending on free acid and hydroxyl groups on the reactants, were used so that accessible amount of base for the Suzuki reaction itself was 3 eq (Schemes 7 and 8).…”