Publications

Selective mono-α-arylation of the simplest ketone, acetone, is a highly sought-after yet challenging transformation. Herein, we present a Pd-catalyzed three-component cascade approach that achieves mono α-arylation of acetone at room temperature. The ligand was crucial in accomplishing the reaction at room-temperature. This methodology enabled a diverse range of difunctionalized biarylated products in good to excellent yields, accomplished by reacting cyclic diaryliodoniums with alkenes and acetone. Mechanistic studies indicate that the alkenylation plays a crucial role in the a-arylation of acetone, likely stabilizing the Pd-complex and enabling the cascade reaction with acetone. A gram-scale reaction and further synthetic manipulations have been demonstrated. 

The construction of complex molecules under metal-free conditions via multiple bond-forming steps in a cascade manner is highly desirable. Herein, we have developed an HFIP-alone promoted aminomethylation and intramolecular cyclization of allenamides, providing biologically relevant tetrahydro-b-carboline derivatives embedded with an allylic amine functionality. The metal-free protocol provided the desired tetrahydro-b-carboline derivatives under mild conditions. The potential of the protocol is further highlighted by the gram-scale reaction and synthesizing derivatives of biologically important molecules.

Biaryl motifs are essential structural features in several drugs and functional molecules. Cyclic diaryliodonium has been scarcely explored as a bifunctional agent compared to ring opening and annulation reactions. Herein, a three-component cascade approach is developed to synthesize bifunctionalized biaryls employing cyclic diaryliodoniums as a biarylating agent. The mild conditions enabled a vast array of biarylated products in good yields in a single step. Furthermore, preliminary mechanistic details and photophysical properties have been investigated.

Cascade dearomative functionalization is a robust protocol to convert flat arenes into medicinally relevant three-dimensional architectures with added new functionality. Herein, a dearomative cycloaddition protocol for synthesizing tetrahydroquinoline-embedded α-tertiary amine scaffolds has been developed employing quinolinium salts and sulfonyl azides under metal-free conditions. An underexplored and mechanistically distinct pathway is unveiled, creating quaternary-center-bearing amine skeletons by an amine group migration during the transfer hydrogenation and cycloaddition cascade reaction. This approach provided a broad substrate scope of α-tertiary amine scaffolds from a plethora of C3-substituted quinolinium and sulfonyl azides. The post-synthetic modifications have further diversified the α-tertiary amine core into interesting scaffolds. Preliminary mechanistic studies suggested the involvement of aziridine ring formation for the amine migration to the C-3 position of quinoline to generate the α-tertiary amine core.

The construction of biologically interesting N-heterocycles under metal-free conditions is a constant goal in industry and academia. Herein, we have developed an HFIP-mediated intramolecular cyclization of allenamides, providing tetrahydro-b-carboline derivatives embedded with a C1-vinyl functionality. The metal-free protocol provided tetrahydro-b-carboline derivatives atom-efficiently under room temperature with a broad substrate scope in good to excellent yields. The potential impact of the protocol is further highlighted by synthesizing derivatives of biologically important molecules and diversified scaffolds via post-synthetic modifications.

The chemoselective N-H insertion of unsymmetrical diamines into carbene is a longstanding challenge. A simple copper-catalyzed strategy for synthesizing C-substituted piperazinones is described, employing easily accessible diazo compounds and 1,2-diamines. The reaction proceeded via chemo-selective carbene insertion at the comparatively less nucleophilic amine, followed by instantaneous cyclization. The protocol was further extended to access NH-free piperazinone, and the synthesis of a Mianserin derivative. 

Incorporating fluorinated moieties into organic molecules is an attractive strategy to enhance drug-like properties. Herein, we have developed a simple and self-promoted protocol for hexafluoroisopropoxylation and trifluoroethoxylation of allenamides with fluorinated alcohols such as HFIP and TFE. The reaction provided the fluoroalkoxylated products in a regio and stereoselective manner in good to moderate yields under mild conditions.   

Easy access to divergent products with chemoselectivity is of great importance in organic synthesis. Herein, we have developed a chemoselective copper-catalyzed carbene insertion protocol onto N-H bonds of tryptamine derivatives. Divergent insertion products are obtained by varying the nucleophilicity of the aliphatic NH of tryptamine with electron-donating or electron-withdrawing groups. The reaction provided N-H insertion products with broad substrate scope in good yields. 

The difficulty in isolating cyclic enamines emanating from their intrinsic instability has impeded their exploration in cycloaddition reactions. Here, we achieved a metal-free domino reaction providing quinoline and isoquinoline-derived cyclic amidines by the cycloaddition of azides with in situ generated enamines via dearomatization. 

Bio-derived ethanol is a promising green and sustainable hydrogen-donor solvent. Herein, we have developed Ir-catalyzed transfer hydrogenation of ketones and aldehydes using ethanol as a hydrogen source with amides as simple ligands. Furthermore, the alkylation of ketones and tandem alkylation/transfer hydrogenation of acetophenones is reported with ethanol.    

A domino reaction sequence of cyclopropanation/ring-opening/iminium cyclization of tryptamine derivatives with donor-acceptor diazo compounds is developed to furnish pyrroloindolines creating three consecutive stereogenic centers in a single step. The copper-catalyzed reaction provided pyrroloindolines at room-temperature with good substrate scope.

Herein, we have developed the cyclic diaryliodonium salts as biarylating agents in the C(sp3)-H functionalization using 8-methyl quinoline as the intrinsic directing group. The oxidant-free reaction produces a vast array of the biarylated products with iodo-functionality which can be further functionalized. Additionally, intramolecular C(sp3)-H functionalization in a step-wise manner under palladium-catalyzed conditions produced the fluorene derivatives in excellent yields. 

A mild, palladium-catalyzed domino Heck-cyclization/alkoxylation sequence of aryl halide tethered allenamides is described, providing regiodivergent indole and indoline derivatives controlled by the N-protecting group. This room temperature reaction provided functionalizable olefinic moiety with broad substrate scope. Preliminary mechanistic studies support the rearrangement of indoline derived intermediate to indoles with the N-acetyl allenamides forming free (NH) indoles. 

Catalytic transfer hydrogenation (TH) for the reduction of heterocycles is an emerging strategy for accessing biologically active saturated N-heterocycles. Herein, we report a TH protocol that utilizes ethanol as a renewable hydrogen source and an Ir catalyst for the reduction of quinolines and pyridines. The reaction is promoted by simple amides as ligands. 

A palladium-catalyzed domino Heck/intermolecular direct hetero arylation sequence of unactivated alkenes was developed, providing 1,2,3-triazole containing bisheterocycles bearing all-carbon quaternary centers with yields of 25–90%. The protocol was extended to 1,3,4-oxadiazoles as well. The installed triazole was further exploited for late-stage functionalizations, and the mechanistic studies indicate the involvement of C–H activation. 

Extended π-conjugated small polycyclic aromatic hydrocarbons (PAHs), nanographenes and graphene nanoribbon (GNR) molecules find wide applications in materials chemistry owing to their exceptional physical and optical properties. Apparently, extensive research interest has been focused on the efficient synthesis of these molecules. In this review, recent developments by C-H functionalization strategies that can efficiently control the crucial size and edge configurations have been discussed. 

Herein, we report the first Cu‐catalyzed one‐step method for the synthesis of 1,2,4‐oxadiazoles from stable, less toxic, and readily available amides and organic nitriles by a rare oxidative N–O bond formation using O2 as sole oxidant. This method has a broad substrate scope and a good tolerance for diverse functional groups. Moreover, the synthetic utility of this method is highlighted by the synthesis of biologically active 3,5‐disubstituted derivatives.