Palladium-Catalyzed C–H Arylation of Benzofurans with Triarylantimony Difluorides for the Synthesis of 2-Arylbenzofurans

Abstract

Pd-catalyzed regioselective C–H arylation is a useful tool for the chemical modification of aromatic heterocycles and 2-arylbenzofuran derivatives are of interest as biologically active substances. Herein, the reaction of triarylantimony difluorides with benzofurans under aerobic conditions in 1,2-DCE, using 5 mol% Pd (OAc)2 and 2 eq. of CuCl2 at 80 °C, produced a variety of 2-arylbenzofurans in moderate-to-high yields. The reaction is sensitive to the electronic nature of the substituents on the benzene ring of the triarylantimony difluorides: an electron-donating group showed higher reactivity than an electron-withdrawing group. Single crystal X-ray analysis of tri(p-methylphenyl) antimony difluoride revealed that the central antimony atom exhibits trigonal bipyramidal geometry.

Direct α-Arylation of Benzo[b]furans Catalyzed by a Pd3 Cluster

“…Deuterated substrate 1a-D was treated under the standard conditions (Scheme -ii), and no deuterium scrambling was observed in product 1a , suggesting that a reversible concerted metalation–deprotonation process is unlikely to occur in the reaction. ,,,− Furthermore, a kinetic isotope effect (KIE) study was conducted, and the small magnitude of KIE (1.17) showed that the cleavage of the C–H bond is unlikely to be involved in the rate-determining step (Scheme -iii). ,,,− Beyond the CMD mechanism, an S E Ar mechanism at the C-2 site of benzofuran followed by reductive elimination and rearomatization ,,, or an electrophilic attack of cationic palladium followed by aryl ligand migration seem more likely to be responsible for the reaction, which is consistent with the results of deuterium scrambling and the KIE studies. In addition, the Heck-type mechanism might also be possible, as demonstrated by many others. ,,,,,, Finally, although we cannot rule out the possibility of the Pd 3 cluster acting as a reservoir to in situ generate some mononuclear Pd species or nanoparticles, the ultraviolet–visible (UV–vis) spectra of the solution in the reaction process (Scheme -iv) showed that the Pd 3 Cl absorption spectrum remained essentially unchanged over the reaction course, indicating that the Pd 3 cluster core might not undergo substantial change or decomposition during catalysis.…”

“…In addition, the Heck-type mechanism might also be possible, as demonstrated by many others. 57,59,60,63,64,68,74 Finally, although we cannot rule out the possibility of the Pd 3 cluster acting as a reservoir to in situ generate some mononuclear Pd species or nanoparticles, the ultraviolet−visible (UV−vis) spectra of the solution in the reaction process (Scheme 3-iv) showed that the Pd 3 Cl absorption spectrum remained essentially unchanged over the reaction course, 31 indicating that the Pd 3 cluster core might not undergo substantial change or decomposition during catalysis.…”

“…The benzofuran skeletons are important structural motifs found in both natural products and pharmaceutical molecules. − Among these benzofuran ring systems, 2-arylbenzofurans exhibit a broad range of biological activities, and many methods have been developed to construct this important structure. , In this context, the direct C–H arylation strategy has been used as one of the most powerful protocols for the synthesis of 2-arylbenzofurans, and a wide variety of aryl electrophiles have been employed as effective coupling partners, including aryl chloride, arenes, arylboronic acids, diaryliodonium salts, benzenesulfonyl chlorides, aryldiazonium salts, , N ′-acyl arylhydrazines, triarylantimony difluorides, and aryl iodides. − Molecular catalysts based on mono-Pd complexes have been predominant in this type of C–H arylation reaction, while the catalytic behaviors of polynuclear palladium clusters remain virtually unexplored so far to our knowledge.…”

Exploiting the Combination of Displacement and Chemical Plating for a Tailored Electroless Deposition of Palladium Films on Copper

“…The importance of palladium lies in its unique ability to adsorb hydrogen and catalyse hydrogenation and dehydrogenation reactions. Palladium plays a fundamental role in a wide range of applications: in the energy field for the production [1], storage [2] and use of hydrogen in catalytic fuel cells [3][4][5], and even in the chemical synthesis field with applications in optoelectronics [6] and biology [7,8]. It is estimated that it is the element with the highest hydrogen adsorption capacity, managing to store volumes equal to 935 times its own [9].…”