Novel hexadentate imidazolium salts in the rhodium-catalyzed addition of arylboronic acids to aldehydes

Four novel hexadentate imidazolium salts were synthesized from hexakis(bromomethyl)benzene and 1-substituted imidazole. The arylation of aldehydes with arylboronic acids was effected conveniently and in high yields by a catalyst system generated in situ from these hexadentate imidazolium salts, [Rh(COD)Cl]₂ and a base.     

Tetraphenylantimony carboxylates in the cascade Pd-catalyzed C-phenylation reaction of methyl acrylate in the presence of peroxide

Tetraphenylantimony(V) carboxylates have been used in the palladium-catalyzed C-phenylation reaction of methyl acrylate in the presence of (PhCO₂)₂ or t-BuOOH under mild conditions (50 °C). The peroxides promote a cascade participation of the organoantimony compound and result in the transfer of three phenyl groups. Organoantimony intermediates have been isolated from the reaction.     

Synthesis of 5-arylhistidines via a Suzuki-Miyaura cross-coupling

Microwave irradiation efficiently promoted the Suzuki-Miyaura reaction of a 5-bromohistidine with various arylboronic acids in the presence of a palladium catalyst. This methodology allowed the synthesis of histidines substituted at position 5 of the imidazole ring with a phenyl, a substituted phenyl, a pyridyl or a thienyl ring. The corresponding 5-arylhistidines were obtained in moderate to good yields.     

Rhodium-catalyzed addition of arylboron compounds to nitriles, ketones, and imines

The rhodium-catalyzed addition reactions of sodium tetraphenylborate and arylboronic acids to nitriles, ketones, and imines were examined. The reaction of nitriles could be carried out efficiently in the presence of a catalyst system of [RhCl(cod)]₂-dppp and H₂O to give the corresponding monoarylated products selectively. Although unactivated ketones and imines are known to be poor electrophiles for rhodium-catalyzed arylation, the phenylation of them with use of sodium tetraphenylborate proceeded smoothly in the presence of [RhCl(cod)]₂ and Rh(acac)(cod) as catalysts, respectively. The addition of NH₄Cl was found to be crucial to effectively conduct the reaction of ketones and imines.     

Sodium Bismuthate Mediated Oxidation of Allylic and Benzylic Alcohols

A simple and readily available oxidation of primary allylic and benzylic alcohols to the corresponding aldehydes is carried out by sodium bismuthate in acetic acid.     

First Synthesis of 5-Chloro-7-[1,3]oxazolo[4,5-b]pyridin-2-ylquinolin-8-ol by Pd-Catalyzed Arylation

5-Chloro-7-[1,3]oxazolo[4,5-b]pyridin-2-ylquinolin-8-ol was synthesized by a Pd-catalyzed arylation, which proceeds efficiently with 2 equivalents of benzylated clioquinol and 1 equivalent of oxazolo[4,5-b]pyridine. The product was smoothly debenzylated by boron trichloride in dichloromethane.     

Nickel-catalyzed intramolecular C–H arylation using aryl pivalates as electrophiles

This paper describes a method for nickel catalyzed intramolecular C–H arylation using aryl pivalates as electrophiles. The transformation is efficient for the synthesis of diverse electronically and sterically differentiated dibenzofurans. Additionally, the method could be expanded toward the synthesis of carbazoles. Preliminary mechanistic studies of the transformation are also described.     

Synthesis of cis-3-arylated cycloalkylamines through palladium-catalyzed methylene sp carbon–hydrogen bond activation

Methylene sp³ carbon–hydrogen bond activation of N-picolinoylcycloalkylamines provides a useful method for synthesizing cis-3-arylated cycloalkylamine derivatives. Pd(II) species catalyzed the γ-arylation of N-picolinoylcycloalkylamines with aryl iodides in the presence of silver carbonate to afford cis-3-arylated N-picolinoylalkylamines in up to 87% yield. Hydrolysis of the amide linkage to give the corresponding cis-3-arylated cycloalkylamines was also demonstrated.     

Synthesis of 5-alkyl-5-aryl-1-pyrroline N-oxides from 1-aryl-substituted nitroalkanes and acrolein via Michael addition and nitro reductive cyclization

A general method for accessing 5-alkyl-5-aryl-1-pyrroline N-oxides (AAPOs) has been established using readily available aryl bromides, nitroalkanes, and acrolein as the starting materials. The palladium-catalyzed arylation of nitroalkanes gave the 1-aryl-substituted nitroalkanes, which underwent the Et₃N-catalyzed Michael addition with acrolein at room temperature to afford the 4-aryl-4-nitroaldehydes. The latter were then subjected to the nitro reductive cyclization using Zn–HOAc in EtOH at 0 °C followed by warming the reaction mixture to room temperature for 24 h, furnishing the 5-alkyl-5-aryl-1-pyrroline N-oxides in good overall yields. Selected examples of 1,3-dipolar cycloaddition of the cyclic nitrones with methyl methacrylate were also described.     

Metallaphotoredox⁃Catalyzed O⁃Arylation of Serine北大核心CSCD

A metallaphotoredox catalyzed hydroxyl aromatization of serine is developed to achieve rapid synthesis of aryl ethers of various serine derivatives. Under the catalytic system of ethylene glycol dimethyl ether nickel bromide （NiBr2 （dme））/4,4'-dimethoxy-2,2'-bipyridine/zinc powder and synergistic iridium photoredox catalysis, nickel is catalyzed and inserted into the C—Br bond, and then followed by transmetalation with the hydroxyl group of serine. The resulting Ni（Ⅱ）species are oxidized by the excited Ir（Ⅲ）species to a Ni（Ⅲ）intermediate. This intermediate is unstable and reductive elimination takes place rapidly to give the target product O-arylated serine in the yields from 65% to 39%. Through a metallaphotoredox catalysis strategy,the reaction features mild,efficient,clean and broad scope of substrate, providing a new way for the synthesis of various serine derivatives with medicinal value. © 2022, Science Press (China). All rights reserved.