I₂‑Catalyzed Oxidative Coupling Reactions of Hydrazones and Amines and the Application in the Synthesis of 1,3,5-Trisubstituted 1,2,4-Triazoles

A general and expeditious approach for the metal-free mediated synthesis of 1,3,5-trisubstituted 1,2,4-triazoles from hydrazones and aliphatic amines has been achieved under aerobic oxidative conditions. The reaction proceeds through a cascade C–H functionalization, double C–N bonds formation, and oxidative aromatization sequence

Solvent-Controlled, Tunable Hydrosulfonylation of 3‑Cyclopropylideneprop-2-en-1-ones

An interesting and tunable hydrosulfonylation of 3-cyclo­propylidene­prop-2-en-1-ones with sodium sulfinates and acetic acid is described. The corresponding β- or γ-addition products can be produced in good to excellent yields with high selectivities, respectively. A rationale for these transformations is proposed base on the controlled experiments

Ru-Catalyzed Synthesis of Dihydrofuroquinolines from Azido-cyclopropyl Ketones

An efficient Ru-catalyzed synthesis of dihydrofuroquinolines from azido-cyclopropyl ketones via the reduction–cyclization–rearrangement process is reported. A plausible reaction mechanism for this process is depicted. Additionally, when the reaction was carried out under H₂ (1 atm) in the presence of Pd/C, 4-quinolones were obtained in excellent yields

Oxidative Asymmetric [2 + 3] Annulation of Aldehydes with Azomethine Imines Enabled by <i>N</i>‑Heterocyclic Carbene Catalysis

An efficient asymmetric [2 + 3] annulation of simple aldehydes with <i>N</i>,<i>N</i>′-cyclic azomethine imines via oxidative <i>N</i>-heterocyclic carbene (NHC) catalysis is disclosed, affording bicyclic pyrazolidinones bearing two vicinal tertiary stereogenic centers with moderate to good yields (56–84% for 19 examples), good to excellent diastereoselectivities (>20:1 for 17 examples), and good to excellent enantioselectivities (66–98% for 19 examples). This direct α-carbon functionalization reaction of aldehyde can be readily performed on gram scale under mild conditions, and a five-membered transition state is proposed to rationalize the stereochemical outcome

Oxidative Asymmetric [2 + 3] Annulation of Aldehydes with Azomethine Imines Enabled by <i>N</i>‑Heterocyclic Carbene Catalysis

An efficient asymmetric [2 + 3] annulation of simple aldehydes with <i>N</i>,<i>N</i>′-cyclic azomethine imines via oxidative <i>N</i>-heterocyclic carbene (NHC) catalysis is disclosed, affording bicyclic pyrazolidinones bearing two vicinal tertiary stereogenic centers with moderate to good yields (56–84% for 19 examples), good to excellent diastereoselectivities (>20:1 for 17 examples), and good to excellent enantioselectivities (66–98% for 19 examples). This direct α-carbon functionalization reaction of aldehyde can be readily performed on gram scale under mild conditions, and a five-membered transition state is proposed to rationalize the stereochemical outcome

Catalyst-Controlled Chemodivergent Modification of Indoles with 2‑Furylcarbinols: Piancatelli Reaction vs Cross-Dehydrative Coupling Reaction

A divergent synthetic strategy to functionalize the indole nucleus with readily available 2-furylcarbinols was developed. It was found that the 3-(4-<i>oxo</i>-2-cyclopentenyl)­indoles were obtained in moderate to good yields (up to 89%) through Piancatelli reaction catalyzed by ZnCl₂, whereas employment of Brønsted acid TFA afforded directly coupled product 3-(2-furyl)­indoles in moderate to good yields (up to 87%) via the deprotonation–rearomatization route

1,2-Gold Carbene Transfer Empowers Regioselective Synthesis of Polysubstituted Furans

A gold-catalyzed cascade cycloisomerization/ring-opening reaction of allenyl ketones bearing a cyclopropyl moiety with a wide variety of alcohols or ketones is developed. This reaction involves an unprecedented 1,2-gold carbene transfer to provide regioselective and modular access to tri- or tetrasubstituted furans in moderate to high yields and with broad substrate tolerability

Ru-Catalyzed Synthesis of Dihydrofuroquinolines from Azido-cyclopropyl Ketones

An efficient Ru-catalyzed synthesis of dihydrofuroquinolines from azido-cyclopropyl ketones via the reduction–cyclization–rearrangement process is reported. A plausible reaction mechanism for this process is depicted. Additionally, when the reaction was carried out under H₂ (1 atm) in the presence of Pd/C, 4-quinolones were obtained in excellent yields

Bi(OTf)₃-Catalyzed Intramolecular Amination of Triazenylaryl Allylic Alcohols: A Stereoselective, High-Yield Synthesis of (<i>E</i>)-3-Alkenyl 2<i>H</i>-indazoles

<div><p></p><p>An efficient Bi(OTf)₃-catalyzed synthesis of 3-alkenyl-2-pyrrolidine-2H-indazoles from triazenylaryl allylic alcohols via the intramolecular direct amination process is reported. Compared with the dodecyl benzenesulfonic acid (DBSA)-catalyzed method, the new method is more efficient and gives greater yields and functionality tolerance. Additionally, the 3-alkenyl-2-pyrrolidine-2H-indazoles can be transformed to a series of new products under different reaction conditions.</p> </div

Brönsted Acid-Mediated Intramolecular Cyclization of Biaryl Triazenes for the Synthesis of Fluorenes and 9,10-Dihydro-Phenanthrenes

The efficient synthesis of fluorenes from biaryl triazenes is successfully developed. Up to 27 examples of biaryl triazenes are converted into their corresponding fluorene derivatives in the presence of CF₃COOH (4.0 equiv). Mechanism research indicates that the reaction undergoes concerted processes, and pentacoordinate carbocations may be involved in these reactions