Synthesis of Quinolines and 2‐Functionalized Quinolines by Difluorocarbene Incorporation

Cu-Catalyzed Carbocyclization for General Synthesis of N-Containing Heterocyclics Enabled by BrCF2COOEt as a C1 Source

A practical and efficient copper-catalyzed carbocyclization of 2-functionalized anilines with ethyl bromodifluoroacetate has been developed. Ethyl bromodifluoroacetate is employed as the C1 source via quadruple cleavage in this transformation. This reaction can afford a variety of N-containing heterocyclics with satisfactory yields and excellent functional group compatibility.

Access to 2-thio/selenoquinolines via domino reaction of isocyanides with sulfur and selenium in water

A domino reaction of o-alkenylaryl isocyanides with elemental sulfur and selenium in pure water was developed for the efficient and green synthesis of quinoline-2-thione and diquinolyl diselenide derivatives. Mechanistical investigation reveals that intramolecular nucleophilic addition of an alkenyl group to the in situ generated isothio/isoselenocyanate accounts for the formation of a quinoline-ring. Moreover, this transformation is also amendable for the convenient preparation of 2-fluoromethylthio-/seleno-quinolines by a one-pot three-component reaction.

Difluoromethylation-Carboxylation and -Deuteration of Alkenes Triggered by Electroreduction of Difluoromethyltriphenylphosphonium Bromide

It is significant to develop novel difluoromethylation methods because of the important roles of difluoromethyl groups in the medicinal chemistry and material industries. Here, we developed a novel difluoromethylation-carboxylation and difluoromethylation-deuteration method triggered by a difluoromethyl radical generated by electroreduction of stable and easily available difluoromethyltriphenylphosphonium bromide. Various molecules containing difluoromethyl and carboxyl or deuterium groups can be synthesized through this method. The establishment of this method will provide an alternative to radical difluoromethylation reactions.

Directed C8-H allylation of quinoline N-oxides with vinylcyclopropanes via sequential C-H/C-C activation

The Rh(III)-catalyzed C8-allylation of quinoline N-oxides has been accomplished using vinylcyclopropanes as an allyl source with excellent diastereoselectivity at room temperature. The C-H/C-C activation, substrate scope and natural product mutation are the important practical features.

2,9-Dimethyl-4H-oxazolo[5’,4’:4,5]pyrano[3,2-f]quinolin-4-one

The new 2,9-dimethyl-4H-oxazolo[5’,4’:4,5]pyrano[3,2-f]quinolin-4-one was successfully prepared through the three-component iodine-catalyzed reaction of n-butyl vinyl ether with the new 8-amino-2-methyl-4H-chromeno[3,4-d]oxazol-4-one. The latter was prepared by the reduction of 2-methyl-8-nitro-4H-chromeno[3,4-d]oxazol-4-one with Pd/C in a hydrogen atmosphere. The above nitro compound was synthesized by the condensation of N-(4-hydroxy-6-nitro-2-oxo-2H-chromen-3-yl)acetamide with P2O5 under microwave irradiation. The above acetamide derivative was prepared during the nitration of 2-methyl-4H-chromeno[3,4-d]oxazol-4-one with H2SO4 and KNO3. The structure of the newly synthesized compounds was confirmed by FT-IR, LC-MS, 1H-NMR, and 13C-NMR analyses. Preliminary biological tests show significant anti-lipid peroxidation activity for the title compound and the other synthesized new intermediates, as well as interesting soybean lipoxygenase inhibition for acetamide 2 (IC50 55 μM) and nitro-compound 3 (IC50 27 μM).

Direct formylation of phenols using difluorocarbene as a safe CO surrogate

A convenient method to prepare aryl formates is reported herein that exploits difluorocarbene to serve as a CO surrogate. This reaction is proposed to occur through a sequential O-difluoromethylation of phenol, followed by α-C-F bond functionalization of the resulting aryl difluoromethyl ether intermediate by phenol or moisture through fluorosemiacetal or orthoformate intermediates. Late-stage modification of biologically and materially active compounds is demonstrated.

Three-Component Coupling of Anilines, Amines, and Difluorocarbene to Access Formamidines

A one-pot three-component reaction of two anilines (or one aniline and one alkylamine) and in situ-generated difluorocarbene is developed herein to enable efficient construction of formamidines. Crucial formimidoyl fluoride intermediate RN═CHF is proposed from the reaction of a primary aniline and difluorocarbene. Ensuing nucleophilic iminyl substitution of this intermediate with a second amine allows cross-condensation of the two amines to produce formamidines. When only one type of primary aniline is used as the substrate, the difluoromethylated homo-condensation products can also be produced under a 1:1 molar ratio of aniline/difluorocarbene. Intramolecular variant of this method allows concise synthesis of benzimidazoquinazolines and nitrogen-fused/spirocyclic compounds, showing the potential of this method in organic synthesis. More interesting reactions are anticipated by exploiting the reactivity of difluorocarbene and primary amines to isocyanides or the formimidoyl fluoride intermediates.