Hongjun Ren

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.

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.

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.

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-oxo-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.

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.

Spontaneous Dimerization of Allenes in Situ: An Efficient Synthesis of Substituted 1,2‐Dimethylenecyclobutanes with High Regio‐ and Stereoselectivities

An intermolecular [2+2] cycloaddition reaction for the synthesis of 1,2-dimethylenecyclobutane derivatives from the commercially available starting materials aryl acetylenes, nBuLi, formamides, and trimethylsilyl cyanide (TMSCN) has been achieved. This reaction displays high regio- and stereoselectivities due to the captodative effect. The mechanism of the reaction has been investigated by the deuterium labeling experiments and DFT calculations.

Lewis Acid Catalyzed Regiospecific Cross-Dehydrative Coupling Reaction of 2-Furylcarbinols with β-Keto Amides or 4-Hydroxycoumarins: A Route to Furyl Enols

Lewis acid catalyzed directly dehydrative carbon-carbon bond formation reaction of 2-furylcarbinols with β-keto amides provides a straightforward method for regioselective synthesis of (Z)-furyl enols. Moreover, this Lewis acid catalyzed cross-coupling reaction can be extended to an interesting heterocyclic version featuring a functionalized 3-furyl-4-hydroxycoumarin synthesis.

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.

A modular approach to highly functionalized 3-sulfonylfurans via conjugate addition of 3-cyclopropylideneprop-2-en-1-ones with sodium sulfinates and sequential 5-endo-trig iodocyclization

A highly efficient conjugate addition and 5-endo-trig cyclization reaction of 3-cyclopropylideneprop-2-en-1-ones with sodium sulfinates in the presence of iodine is described. A wide variety of densely functionalized 3-sulfonylfurans are furnished by single-step and one-pot methods, respectively. The results of such postcyclization modifications are also presented.

Strain-Promoted Nitration of 3-Cyclopropylideneprop-2-en-1-ones and the Application for the Synthesis of Pyrroles

The tunable nucleophilic nitration of 3-cyclopropylideneprop-2-en-1-ones with cheap sodium nitrite is described. This transformation proceeds with the assistance of a strained cyclopropane ring and allows for a divergent route to various synthetically useful β,γ-dinitro or γ-mononitro adducts in high yields with exclusive regio- and stereoselectivity. Additionally, a wide array of valuable functionalized N-unprotected pyrroles is achieved from the resulting β,γ-dinitro compounds via reductive cyclization strategy.