Sajal Das

Efficient, mild and completely regioselective synthesis of substituted pyridines

Addition of Grignard reagents to pyridine N-oxides in THF at low temperature (-78 to -20 degrees C) and treatment with TFAA provides an efficient general procedure for synthesis of substituted pyridines. The method is compatible with a range of functional groups such as esters, halogens and nitriles.

Complete regioselective addition of grignard reagents to pyrazine N-oxides, toward an efficient enantioselective synthesis of substituted piperazines

A conceptually new one-pot strategy for the synthesis of protected substituted piperazines via the addition of Grignard reagents to pyrazine N-oxides is presented. This strategy is high yielding (33-91% over three steps), step-efficient, and fast. The synthesized N,N-diprotected piperazines are convenient to handle and allow for orthogonal deprotection at either nitrogen for selective transformations. In addition, this is a synthetic route to enantiomerically enriched piperazines by using a combination of phenyl magnesium chloride and (-)-sparteine, which resulted in enantiomeric excesses up to 83%.

Formation, thermodynamic properties, microstructures and antimicrobial activity of mixed cationic/non-ionic surfactant microemulsions with isopropyl myristate as oil.

HYPOTHESIS Modification of the interface by blending of surfactants produces considerable changes in the elastic rigidity of the interface, which in turn affects the physicochemical properties of w/o microemulsions. Hence, it could be possible to tune the thermodynamic properties, microstructures and antimicrobial activity of microemulsions by using ionic/non-ionic mixed surfactants and polar lipophilic oil, which are widely used in biologically relevant systems. EXPERIMENTS The present report was aimed at precise characterization of mixed cetyltrimethylammonium bromide and polyoxyethylene (23) lauryl ether microemulsions stabilized in 1-pentanol (Pn) and isopropyl myristate at different physicochemical conditions by employing phase studies, the dilution method, conductivity, DLS, FTIR (with HOD probing) and (1)H NMR measurements. Further, microbiological activities at different compositions were examined against two bacterial strains Bacillus subtilis and Escherichia coli at 303 K. FINDINGS The formation of mixed surfactant microemulsions was found to be spontaneous at all compositions, whereas it was endothermic at equimolar composition. FTIR and (1)H NMR measurements showed the existence of bulk-like, bound and trapped water molecules in confined environments. Interestingly, composition dependence of both highest and lowest inhibitory effects was observed against the bacterial strains, whereas similar features in spontaneity of microemulsion formation were also evidenced. These results suggested a close relationship between thermodynamic stability and antimicrobial activities. Such studies on polar lipophilic oil derived mixed surfactant microemulsions have not been reported earlier.

Physicochemical studies of water-in-oil nonionic microemulsion in presence of benzimidazole-based ionic liquid and probing of microenvironment using model C–C cross coupling (Heck) reaction

The present report focuses on the evaluation of the interfacial composition and the thermodynamics of the transfer of 1-pentanol (Pn) from a continuous oil phase to the interface of w/o nonionic microemulsion [Tween-20/Pn/cyclohexane(Cy)/water] in the absence and the presence of an ionic liquid (IL) (1-butyl-3-propylbenzimidazolium bromide) under different physicochemical conditions [viz. variation in concentrations of IL (0.0 → 0.20 mol dm−3) and temperature (293 → 323 K] at a fixed molar ratio of water to surfactant (ω) by the Schulmans method of cosurfactant titration at the oil/water interface. The overall transfer process has been found to be spontaneous, exothermic and organized in the absence or the presence of IL, but shown to be influenced by [IL]. The microstructure and state of water organization inside a pool of these systems have been characterized by different experimental techniques, e.g., conductivity, DLS and FTIR in the absence or the presence of IL. In addition, a C–C cross coupling reaction (Heck reaction) has been employed to explore the properties of IL (additive) in the confined environment of the microemulsion vis-a-vis its interaction with the constituents of the interface. The reaction progress has been monitored using the above techniques. The reaction ended with the highest yield (75%) in the presence of 0.05 mol dm−3 of IL, wherein the microemulsion forms spontaneously with the highest stability.

Synthesis of 6-aryl substituted 4-quinolones via Suzuki cross coupling

A convenient way to introduce aryl functionalization in the 6-position of 4-quinolones is developed via selective bromination and subsequent arylation by Suzuki cross-coupling. Ethyl 4-quinolone 3-carboxylates were subjected to selective bromination at C-6 followed by arylation under microwave irradiation that yielded the desired cross-coupling products within 5 minutes. This approach can expediently be used for library synthesis of the aryl functionalized 4-quinolone derivative, an important class of biologically active compounds.

Transfer hydrogenation using recyclable polymer-supported formate (PSF) : Efficient and chemoselective reduction of nitroarenes

SummaryNitroarenes can be reduced in high yields to the corresponding anilines by transfer hydrogenation using a stable H-donor, polymer-supported formate (PSF) in combination with palladium acetate (catalytic). The reactions occur at 100–120∘C in dimethyl-formamide and the PSF can be recycled for at least three runs. The procedure is chemoselective for nitro group; ester, ketone, aldehyde, and halide substituents on aromatic ring remain unaffected.

A straight forward synthesis of 4-aryl substituted 2-quinolones via Heck reaction

A variety of aryl halides have been successfully coupled with different olefins via Heck reaction in the presence of an active stimulant (Pd–NHC). An efficient one pot protocol for the easy access of structurally diverse 4-aryl-2-quinolones via domino Heck/cyclization reaction has been developed.

Auto-Tandem Palladium Catalysis: From Isoxazole to 2-Azafluorenone

An auto-tandem palladium catalysis from halogen-substituted isoxazoles and Michael acceptors is described. It involves two mechanistically distinct palladium-catalyzed reactions, a Heck reaction and a rearrangement, leading to 2-azafluorenones. It is the first example of palladium-catalyzed ring opening of isoxazoles and rearrangement of the β-imino ketone ring-opening product.

Chemoselective reduction of aldehydes by ruthenium trichloride and resin-bound formates

Summary A simple, chemoselective transfer hydrogenation of aryl aldehydes with the aid of Amberlite® resin formate (ARF), a stable H-donor, in the presence of catalytic ruthenium trichloride is described. Aromatic aldehydes and 1,2-diketones are reduced efficiently and selectively, while aryl ketones remain unchanged. Several other potentially reducible groups attached to the aromatic moiety are unaffected.

A green protocol for the Pd catalyzed ligand free homocoupling reaction of arylboronic acids under ambient conditions

A simple, competent, green pathway has been developed for the Pd catalyzed ligand free homocoupling reaction of arylboronic acids in water under ambient conditions. An efficient reaction environment is generated using a combination of Pd(OAc)2 and ‘green additives’, which exhibited excellent activity and results in high yields of the desired coupled products within 15 minutes.