Sanjay Bhar

Solvent-free synthesis of 4,4-bis-functionalized-1,6-dienes and 1,6-diynes on the surface of neutral alumina

Abstract An improved procedure has been developed for the synthesis of structurally varied 4,4-bis-functionalized-1,6-dienes and 1,6-diynes through regioselective alkylation of active methylene compounds with several unsymmetrical allyl bromides and propargyl bromide on the surface of neutral alumina impregnated with sodium ethoxide or potassium tert-butoxide in the absence of any solvent under environmentally benign conditions.

Remarkable reactivity of pyridinium chlorochromate adsorbed on neutral alumina under solvent-free conditions

Abstract Pyridinium chlorochromate adsorbed on neutral alumina (PCC-Al 2 O 3 ) under solvent-free conditions has been found to oxidize primary aliphatic alcohols to alkyl alkanoates whereas primary benzylic and primary allylic alcohols produce the corresponding aldehydes. Secondary aliphatic and aromatic alcohols produce ketones without isomerization and polymerization of double bonds, overoxidation and other side-reactions.

Pinacol coupling of aromatic aldehydes and ketones.. An improved method in an aqueous medium

Reductive coupling of aromatic aldehydes and ketones leading to 1,2-diols has been achieved with high yield and good diastereoselectivity under environmentally friendly conditions using aluminium powder in the presence of aqueous sodium hydroxide. The notable advantage of the present method seems to be the negligible formation of side products arising mainly due to reduction of the carbonyls to the corresponding alcohols, Cannizzaro reaction and formation of olefins via McMurry coupling. Diaryl ketones have been found to be unreactive under the present conditions. Moreover, the aluminium recovered after the reaction can be reused after washing and drying.

A colorimetric and turn-on fluorescent chemosensor for selective detection of Hg2+: theoretical studies and intracellular applications

A new colorimetric, “turn-on” fluorescent chemosensor (DEAS-BPH) was synthesized for selective and sensitive recognition of Hg2+ ions with no interference from environmentally relevant metal ions in a mixed organo-aqueous medium. It was found that the presence of mercury induced nearly 27-fold fluorescence enhancement. This was attributed to the 1 : 2 metal–ligand complexation, ascertained by a Jobs plot, NMR titration and HRMS studies. A theoretical study was conducted to rationalize the colorimetric sensing behaviour of the probe on the basis of an intramolecular charge transfer (ICT) mechanism. In addition, morphological alteration upon complexation with mercury was explored with the aid of Field Emission Scanning Electron Microscope (FESEM) measurement. Results of MTT assay and fluorescence microscopic studies unveiled that the probe is cell permeable with low cytotoxicity. Furthermore, the reversibility of the sensor and its efficacy to function in a wide range of pH values designated the suitability to image intracellular Hg2+ ions in living HepG2 and Escherichia coli bacterial cells.

Regioselective Aromatic Electrophilic Bromination with Dioxane Dibromide Under Solvent‐Free Conditions

Abstract Highly regioselective ring bromination of aromatic compounds has been accomplished with high yields and good purity using dioxane dibromide (DD) under solvent‐free conditions. Notable features of this methodology include operational simplicity, rapid reactions, excellent control over the degree of bromination, and tolerance of various functional groups during the reaction.

Highly Selective Regeneration of Carbonyl Compounds from Their Oximes and Semicarbazones in Aqueous Medium

Abstract Chemoselective regeneration of aryl alkyl ketone, α‐tetralone, and cycloalkanone by hydrolysis of their oximes and semicarbazones has been accomplished using aqueous phosphoric acid without involvement of any organic cosolvent in the reaction medium, where the similar derivatives of aryl aldehyde, diaryl ketone, aliphatic acyclic aldehyde and ketone remain mostly inert.

Systematic investigations on the reduction of 4-aryl-4-oxoesters to 1-aryl-1,4-butanediols with methanolic sodium borohydride

Summary 4-Aryl-4-oxoesters undergo facile reduction of both the keto and the ester groups with methanolic NaBH4 at room temperature to yield the corresponding 1-aryl-1,4-butanediols whereas 4-alkyl-4-oxoesters furnish the corresponding 1,4-butanolides via selective reduction of the keto moiety. Results of a detailed and systematic investigation of the reaction are described.

Dioxane dibromide mediated bromination of substituted coumarins under solvent-free conditions.

Summary An efficient solvent-free protocol for regioselective bromination of substituted coumarins has been developed by using dioxane dibromide as the solid brominating agent. The efficacy of the solvent-free protocol has been established. The effects of the electronic nature and location of the substituents on the outcome of the reaction have been rationalized with a proposed mechanism.

Microwave-assisted ammonium formate-mediated Knoevenagel reaction under solvent-free conditions – a green method for C–C bond formation

Abstract Syntheses of structurally varied densely functionalized olefins have been accomplished (23 examples) through microwave-assisted ammonium formate-mediated Knoevenagel condensation of differently substituted aromatic aldehydes with ethyl cyanoacetate, cyanoacetamide, malononitrile, and malonic acid under solvent-free condition in good yield (76–95%) and high purity. The said reactions occur within very short period of time (0.75–3 min) in eco-friendly conditions involving an operationally simple procedure, eliminating any kind of inorganic support, toxic reagent and organic solvent.

Microwave-assisted ammonium formate-mediated synthesis of Hanstzch dihydropyridines under solvent-free conditions – a green protocol

Abstract Microwave-assisted ammonium formate-mediated eco-friendly synthesis of structurally varied Hantzsch dihydropyridines under solvent-free conditions has been successfully accomplished with good yield, minimization of toxic reagents and organic solvents in the process. The elimination of the inorganic support decreased the disposal problem and the extremely small reaction time minimized energy dissipation.