Keshav Raghuvanshi

Expedient C-H amidations of heteroaryl arenes catalyzed by versatile ruthenium(II) catalysts.

Heteroaryl-substituted arenes and heteroarenes were efficiently amidated through ruthenium-catalyzed C-H bond functionalizations with a variety of sulfonyl azides. Particularly, cationic ruthenium(II) complexes proved to be most effective and allowed nitrogenations of electron-rich and electron-deficient arenes with ample substrate scope.

Ruthenium Oxidase Catalysis for Site‐Selective C–H Alkenylations with Ambient O2 as the Sole Oxidant

Ruthenium(II) oxidase catalysis by direct dioxygen-coupled turnover enabled step-economical oxidative C-H alkenylation reactions at ambient pressure. Versatile ruthenium(II) biscarboxylate catalysts displayed ample substrate scope and proved applicable to weakly coordinating and removable directing groups. The twofold C-H functionalization strategy was characterized by exceedingly mild reaction conditions as well as excellent positional selectivity.

Ruthenium(II)-Catalyzed Decarboxylative C−H Activation: Versatile Routes to meta-Alkenylated Arenes

Ruthenium(II) bis(carboxylate)s proved highly effective for two decarboxylative C-H alkenylation strategies. The decarboxylation proceeded efficiently at rather low temperatures. The unique versatility of the decarboxylative ruthenium(II) catalysis is reflected in the oxidative olefinations with alkenes as well as the redox-neutral hydroarylations of alkynes.

Catalyst-free one-pot four-component domino reactions in water–PEG-400: highly efficient and convergent approach to thiazoloquinoline scaffolds

A cost-effective and eco-friendly straightforward synthesis of highly diversified thiazoloquinoline scaffolds is successfully achieved via one-pot four-component cascade reaction utilizing α-enolic dithioesters, cysteamine, aldehydes, and cyclic 1,3-diketones in water–PEG-400. The new efficient domino protocol generates two rings by the concomitant formation of C–C (two), C–N (two), and C–S multiple bonds presumably involving a sequence of N,S-acetal formation, Knoevenagel reaction, aza–ene reaction, imine–enamine/keto–enol tautomerization, and N-cyclization as key steps. The merit of this protocol is highlighted by its easily available and economical starting materials, operational simplicity, efficient utilization of all the reactants, clean reaction profile, simple workup procedure, and tolerance of a wide variety of functional groups.

Ruthenium(II)-Catalyzed C-H Oxygenations of Reusable Sulfoximine Benzamides

C-H oxygenations of synthetically meaningful sulfoximine benzamides were accomplished by a versatile ruthenium catalysis regime. The ruthenium(II) catalyst was characterized by excellent mono- and chemoselectivity as well as positional selectivity via facile base-assisted intramolecular electrophilic substitution-type (BIES) C-H activation. The synthetic utility of the approach was reflected by high functional group tolerance and sulfoximine removal in a traceless fashion.

Ruthenium(II)‐Catalyzed CH Acyloxylation of Phenols with Removable Auxiliary

Intermolecular C-H acyloxylations of phenols with removable directing groups were accomplished with a versatile ruthenium catalyst. Specifically, a cationic ruthenium(II) complex, formed in situ, enabled the chemoselective C-H oxygenations of a broad range of substrates. The catalyst proved tolerant of synthetically valuable functional groups, and the substrate scope included both (hetero)aromatic and, the more challenging, aliphatic carboxylic acids. The proposed reaction mechanism involves a reversible C-H ruthenation and an oxidatively induced C-O-bond-forming reductive elimination.

Eco-efficient, regioselective and rapid access to 4,5-disubstituted 1,2,3-thiadiazoles via [3 + 2] cycloaddition of α-enolicdithioesters with tosyl azide under solvent-free conditions

An efficient, sustainable, and regioselective one-pot synthesis of hitherto unreported 4-aroyl/hetaroyl/alkanoyl-5-alkyl/allyl/benzylsulfanyl-1,2,3-thiadiazoles has been achieved by [3 + 2] cycloaddition of α-enolicdithioesters with tosyl azide through cascade 1–2 (S–N) and 3–4 (C–N) bond connections involving Wolff-type heterocyclization. Optimally, the reactions are very fast and completed within 2–15 minutes, when a mixture of α-enolicdithioester and tosyl azide was stirred at 0 °C in the presence of Et3N under solvent-free conditions. Furthermore, no co-catalyst or activator is necessary. The eco-compatibility, mild conditions, excellent yields, easy purification, and avoidance of expensive/toxic reagents are advantages of this protocol to access this medicinally privileged substructure.

DMAP mediated one-pot domino thienannulation: a versatile, regioselective and green mechanochemical route to naphtho[2,3-b]thiophenes

Solvent-free mechanochemical route to naphtho[2,3-b]thiophenes via [3 + 2] oxidative heteroannulation of α-enolicdithioesters and β-oxothioamides with 1,4-naphthoquinone has been achieved at room temperature.

DMAP-promoted domino annulation of β-ketothioamides with internal alkynes: a highly regioselective access to functionalized 1,3-thiazolidin-4-ones at room temperature

DMAP-mediated rapid and efficient one-pot regioselective access to functionalized 1,3-thiazolidin-4-ones via annulation of β-ketothioamides with internal alkynes has been achieved under mild reaction conditions. The merit of this straightforward domino protocol is highlighted by its operational simplicity, short reaction time, tolerance of a large variety of functional groups, and efficiency of producing two new bonds (C–S and C–N) and one thiazolidine ring.