Sabuj Kundu

An electron defficient porous Co-SAC is developed for the electrophilic olefin cyclopropanation with the involvement of donor/acceptor carbene precursor.

Herein, we report a reusable UiO-67-Pd catalyst for additive-free transfer hydrogenation of epoxides at room temperature using ammonia borane as the hydrogen source. The protocol enables selective conversion of aromatic and aliphatic epoxides into the corresponding alcohols and can be readily applied to the reduction of other unsaturated functionalities, including α,β-unsaturated ketones, N-heterocycles, azoarenes, and nitroarenes. A series of mechanistic investigations were carried out to understand the catalytic process.

Harnessing key intermediates in metal-catalyzed reactions enables highly selective organic transformations. Herein, we report an Ir(III)-catalyzed strategy for the selective synthesis of benzimidazoles and N-methylbenzimidazoles from diverse 2-nitroanilines and 1,2-diaminobenzenes using methanol. Solvent-controlled stabilization of the imine intermediate governed product selectivity: TFE favored benzimidazole formation, whereas methanol promoted rapid hydrogenation to N-methylbenzimidazoles. Mechanistic studies, supported by control experiments and DFT calculations, revealed the crucial role of solvent-modulated hydrogen transfer from a proton-responsive Ir-H species.

An elevated Lewis acid (Zn)-functionalized Co-SAC is developed for selective N–O bond activation of N -alkoxy amides and sulfonamides under mild conditions.

The polarity of radical intermediates dictates their innate reactivity, making polarity‐matched radical couplings inherently favored, while polarity‐mismatched variants remain a formidable challenge. Here, we demonstrate a redox‐neutral, Mg ²⁺ ‐driven strategy that enables efficient coupling of electrophilic radicals with electron‐deficient alkenes without the need for alkene activation or polarity inversion. Crucially, Mg ²⁺ plays a nontraditional mechanistic role: rather than functioning as classical Lewis acidic activator, it acts as a spatial organizer and aligns the transient radical partners to override their intrinsic polarity‐mismatch. Using this approach, we have developed a step‐economical, three‐component tandem synthesis of thioester‐functionalized oxindoles using feedstock aldehydes, elemental sulfur as a sustainable and readily available sulfur source, thereby avoiding prefunctionalized sulfur reagents and multiple steps. The protocol was further applied for the hetero‐annulation of 1,7‐enynes utilizing elemental sulfur for the synthesis of polycyclic compounds, where acyl radical functions as an effective sulfur atom carrier. In addition to several mechanistic studies, theoretical calculations were conducted to support our hypothesis and clarify the mechanism. DFT calculations revealed that redox‐neutral Mg ²⁺ lowers the radical addition free energy barrier by simultaneously coordinating to both reacting partners, steering them into a spatial arrangement that promotes out‐of‐plane orbital overlap, essential for efficient C–S bond formation.

Employing 3d-metal hydrides in hydrogen-transfer catalysis with water as a supplementary reagent remains in its infancy. Herein, we report a phosphine-free Mn(I)-bisNHC system that mediates methyl formate dehydrogenation in water, enabling chemoselective transfer hydrogenation of olefinic bonds in diverse aryl acrylonitriles and phenyl enones and carbonyl groups in α,β-epoxy ketones. Combined experimental and DFT studies reveal base-assisted Mn-H formation from MF/H₂O and substrate-driven electronic effects governing selectivity, establishing a robust platform for aqueous hydrogen-transfer transformations.

Anti-Markovnikov hydrophosphinothiolation of alkenes is quite challenging and is rarely explored. Herein, we report a visible-light-mediated metal-free multicomponent coupling strategy for the anti-Markovnikov hydrophosphinothiolation of styrenes, utilizing readily accessible phosphine-oxides and elemental sulfur. This operationally simple protocol delivers a broad range of S-alkyl-phosphinothioates with excellent selectivity and atom economy. Fine-tuning the reaction parameters tweaks the pathway to afford β-keto-phosphinothioates, expanding the synthetic utility of this transformation to access chemodivergent products.

Visible light-mediated, multicomponent, regioselective phosphinylalkylation of indoles with readily available carbonyl compounds and diaryl phosphine oxides at ambient temperature is demonstrated. The strategy presented here is also effective with anilines. Key to this transformation is the electron-donor-acceptor (EDA) complex formation between the in situ generated (vinylogous) iminium intermediate and secondary phosphine oxides. Mechanistic studies supported the EDA complex-enabled radical pathway.

The selective functionalization of indoles using methanol via borrowing hydrogen (BH) and interrupted borrowing hydrogen (I‐BH) pathways offers a sustainable approach to access value‐added molecules. Herein, the synthesis of a series of benzimidazole‐functionalized cyclometalated (NC)‐Ru(II) and (NN)‐Ru(II) complexes and their application in the chemodivergent functionalization of indoles with methanol are reported, affording either C3‐methylated indoles or bis(indolyl)methanes (BIMs). The product selectivity was governed by the hydricity of the Ru–H species, which was effectively tuned by ligand backbone modification. This varying catalytic behavior of these complexes under consideration toward the selective formation of different products was fairly understood by analyzing their electronic properties based on electrochemical and density functional theory studies. Additionally, the electron‐rich (NC)‐Ru complex facilitated the α‐methylation of phenylacetonitrile under relatively mild conditions. Finally, an array of control experiments and the identification of different intermediates aided in establishing the proposed mechanism.