Palladium‐Catalyzed C–H Acylation of Arenes Using Thioethers as Directing Groups

Abstract

A highly efficient protocol for regioselective synthesis of diaryl ketones by palladium‐catalyzed direct acylation of arenes using thioethers as directing groups is reported. The possible pathway of direct acylation between thioethers and α‐oxocarboxylic acids is discussed.

β-Carboline-directed decarboxylative acylation of ortho-C(sp2)–H of the aryl ring of aryl(β-carbolin-1-yl)methanones with α-ketoacids under palladium catalysis

“…In the absence of a catalyst no product formation was observed (entry 12). Reaction in the presence of other Pd-catalysts like PdCl 2 gave lower yield of 3aa whereas Pd(TFA) 2 afforded the product in comparable yield as obtained with Pd(OAc) 2 (entries [13][14]. Varying the reaction temperature revealed that better yield of product was isolated when the reaction was performed at 80 o C as compared to 60 o C or 100 o C (compare entry 9 with entries 15-16).…”

“…2 Later Ge et al reported the Pd-catalysed decarboxylative acylation of acetanilides and 2-aryl pyridines at the orthoposition of the phenyl ring with α-oxocarboxylic acids via ligand-assisted ortho-C(sp2)-H activation in the presence of an oxidant. 3 Subsequently different directing groups including azobenzenes, 4 azoxybenzenes, 5 carboxylic acids, 6 cyclic enamides, 7 O-methyl ketoximes, 8 O-phenyl carbamates, 9 phenylacetamides, 10 2-aryloxypyridines, 11 pyridine-N-oxides, 12 indolines, 13 thioethers, 14 N-nitroso anilines, 15 tetrahydroquinolines 16 and indoles 17 have been used for performing the acylation via ligand-assisted activation of the ortho-C(sp2)-H bond leading to formation of biaryl ketones with high regioselectivities under mild reaction conditions. β-Carboline, a privileged scaffold, is core unit of several natural alkaloids and bioactive compounds endowed with diverse pharmacological properties.…”

Acylation of (Hetero)Arenes through CH Activation with Aroyl Surrogates

“…In 2014, , Kuang and co‐workers reported the use of a thioether as a directing group for the acylation of arenes,55 isolating the desired ketones in good yields (Scheme ). Remarkably, the thioether group was not oxidized in the presence of oxidant during the reaction.…”

Transition Metal‐Catalyzed C−H Bond Functionalizations by Use of Sulfur‐Containing Directing Groups

“…A highly efficient protocol for theregioselective synthesis of diaryl ketones by palladium‐catalyzed direct acylation of arenes using thioethers as directing groups was reported by Kuang and co‐workers (Scheme ) . When they used α‐oxocarboxylic acids as acylation partners, the reaction smoothly afforded the desired diaryl ketone in the presence of Pd(OAc) 2 (5 mol%) and Ag 2 CO 3 (2 equiv.)…”