Yajun Li

Au(I)-catalyzed intramolecular hydroamination of the fluorinated N'-aryl-N-propargyl amidines: mild conditions for the synthesis of 2-fluoroalkyl imidazole derivatives.

The gold(I)-catalyzed synthesis of 2-fluoroalkyl imidazole derivatives was developed. Catalyzed by gold(I), propargyl amidines underwent a 5-exo-dig cyclization to afford 2-fluoroalkyl-5-methyl imidazoles. Also, 2-fluoroalkyl imidazole-5-carbaldehydes were obtained in the presence of NIS. A mechanism investigation manifested the probable process and the carbonyl oxygen derived from O(2).

Gold(I)-Catalyzed Aminohalogenation of Fluorinated N′-Aryl-N-Propargyl Amidines for the Synthesis of Imidazole Derivatives under Mild Conditions

A procedure for the synthesis of fluorinated imidazole derivatives from propargyl amidines has been developed. Under gold(I) catalysis, propargyl amidines were converted into 5-fluoromethyl imidazoles in the presence of Selectfluor through a cascade cyclization/fluorination process. In contrast, imidazole-5-carbaldehydes were obtained in high yields when N-iodosuccinimide (NIS) was used as the halogenating reagent. The polarity of the solvent and light had significant impact on the formation of the carbaldehydes. These transformations showed excellent functional-group tolerance. An unfluorinated substrate with an electron-withdrawing group also underwent aminohalogenation to give the corresponding product in good yield. Mechanistic investigation revealed the general pathways of these transformations.

Synthesis of Fluorine-Containing Multisubstituted Phenanthridines by Rhodium-Catalyzed Alkyne [2+2+2] Cycloaddition and Tandem sp2 CH Difluoromethylenation

A highly efficient method for the synthesis of fluorine-containing multisubstituted phenanthridines through Rh-catalyzed alkyne [2+2+2] cycloaddition reactions has been developed. This method exhibits excellent functional-group compatibility. When a bromodifluoromethyl group, rather than a trifluoromethyl group, was employed in the cycloaddition reaction, more-complicated polycyclic compounds were obtained through tandem Rh-catalyzed cycloaddition/C-H difluoromethylenation. This route provides convenient access to fluorine-containing polycyclic compounds.

Direct isoperfluoropropylation of arenediazonium salts with hexafluoropropylene

An efficient copper-promoted isoperfluoropropylation of aryl diazonium salts is described. The reaction occurs under mild conditions using commercially available hexafluoropropylene (HFP) as the starting material. In addition, a one-pot direct diazotization and isoperfluoropropylation protocol was developed. The method allows facile conversion of various arylamines into isoperfluoropropylarenes with good functional group compatibility using HFP.

Cu-catalyzed tandem reactions of fluorinated alkynes with sulfonyl azides en route to 2-trifluoromethylquinolines

A novel method for the synthesis of 2-trifluoromethylquinolines via Cu-catalyzed tandem reactions was reported. A strong electronic effect was observed, but the steric effect was negligible.

γ-Amino Butyric Acid (GABA) Synthesis Enabled by Copper-Catalyzed Carboamination of Alkenes

γ-Amino butyric acid (GABA) is the chief inhibitory neurotransmitter in the mammalian central nervous system. Many GABA derivatives are used clinically to prevent or treat neurodegenerative diseases. Copper-catalyzed carboamination of alkenes offers an efficient method to fashion the core structure of GABA derivatives from alkenes. In this reaction, acetonitrile serves as the source of the carbon and nitrogen functionalities used to difunctionalize alkenes. Experimental and density functional theory (DFT) studies were carried out to investigate the mechanism of the reaction, and a copper-catalyzed radical-polar crossover mechanism is proposed.

Iron-Catalyzed Radical Decarboxylative Oxyalkylation of Terminal Alkynes with Alkyl Peroxides

An iron-catalyzed oxyalkylation of alkynes with alkyl peroxides as the alkylating reagents has been investigated. Alkyl peroxides are readily available from aliphatic acids and serve simultaneously as the alkylating reagents and internal oxidants. Primary, secondary, and tertiary alkyl groups of aliphatic acids were readily incorporated into C-C triple bonds and diverse α-alkylated ketones were synthesized. Mechanism studies revealed that this reaction involves highly reactive alkyl free radicals. A unique equilibrium between lauric acid and water catalyzed by the iron(III) catalyst was observed.

Alkyl-Esterification of Vinylarenes Enabled by Visible-Light Induced Decarboxylation

A decarboxylative alkyl esterification of vinylarenes induced by visible light is described. A variety of alkyl diacyl peroxides synthesized from readily available aliphatic carboxylic acids are used as not only the oxygenation but also alkylation source. This simple and easy to handle reaction has a wide substrate scope, excellent yields, and works under mild reaction conditions. Carbon dioxide is the sole byproduct. An oxidative quenching process is proposed as the mechanism.

HOTf-Catalyzed Alkyl-Heck-type Reaction

Summary The Heck reaction, along with other cross-coupling reactions, led to a revolution in organic chemistry. In the last 50 years, metal-catalyzed, photo-induced, or base-mediated Heck and Heck-type reactions have been elegantly developed. Brønsted acid-catalyzed Heck (or Heck-type) reactions are still unknown, however. By introducing alkyl peroxides as the key intermediates, primary, secondary, and tertiary aliphatic carboxylic acids are therefore applied here in a one-pot Brønsted acid-catalyzed Heck-type reaction, to deliver E-alkenes exclusively in most cases. The use of HOTf is vital to the reaction, whose mechanism is supported by both experimental and computational results. This method can be expanded to the direct alkylation of complex natural products.

Metal-free intermolecular aminochlorination of unactivated alkenes

We report a metal-free method for the synthesis of vicinal chloroamines by intermolecular aminochlorination of unactivated alkenes. This regioselective reaction is inexpensive, atom economical, and environmentally benign and tolerates various functional groups. The aminochlorinated product can be easily deprotected and subsequently transformed into valuable compounds.