Pravin R. Likhar

Trifunctional N,N,O-Terdentate Amido/Pyridyl Carboxylate Ligated Pd(II) Complexes for Heck and Suzuki Reactions

Trifunctional N,N,O-terdentate amido/pyridyl carboxylate Pd(II) complexes were highly active and stable phosphine-free catalysts for Heck and room-temperature Suzuki reactions with high turnover numbers up to ca. 10(4).

N4-tetradentate dicarboxyamidate/dipyridyl palladium complexes as robust catalysts for the Heck reaction of deactivated aryl chlorides.

Structurally well defined and thermally stable Pd(II) complexes, derived from N4-tetradentate dicarboxyamide/dipyridyl ligands, were evaluated as catalysts for the Heck reactions of deactivated aryl chlorides and olefins (see scheme). The concept of using an anionic carboxyamide as an ancillary ligand for palladium demonstrated here provides a new opportunity for the development of phosphine-free transition-metal catalysis.

An efficient copper-aluminum hydrotalcite catalyst for asymmetric hydrosilylation of ketones at room temperature

A catalyst system consisting of a copper-aluminum hydrotalcite-chiral diphosphine ligand effects asymmetric hydrosilylation of several ketones, using polymethylhydrosiloxane (PMHS) as the stoichiometric reducing agent at room temperature, with moderate-to-excellent enantioselectivities. The catalyst is recovered by simple centrifugation, and the efficiency of the catalyst remains almost unaltered even after several cycles.

High surface and magnetically recoverable mPANI/pFe3O4 nanocomposites for C–S bond formation in water

A high surface area mPANI/pFe3O4 nanocomposite from mesoporous polyaniline and porous magnetic Fe3O4 was used as a catalyst in the S-arylation of thiophenol with aryl chlorides and in the C–S bond formation between aryl iodides and thiourea in water. The mesoporosity of the polyaniline enhances the efficiency and stability of the porous magnetic Fe3O4 nanoparticles in both coupling reactions. The mPANI/pFe3O4 nanocomposite can be recovered with an external magnet and reused several times due to the superparamagnetic nature of the porous Fe3O4 nanoparticles.

Bis(cyclopentadienyl)zirconium dichloride: an efficient catalyst for highly selective formation of β-alkoxy alcohols via ring opening of 1,2-epoxides with alcohols

Bis(cyclopentadienyl)zirconium dichloride catalyzed ring-opening reactions of epoxides derived from styrene, cyclohexene, norbornene and stilbene, in the presence of primary, secondary, tertiary, cyclohexyl, allyl and propargyl alcohols, resulted in the formation of β-alkoxy alcohols in good to excellent yields with high regio- and stereoselectivity.

Base-mediated chemo- and stereoselective addition of 5-aminoindole/tryptamine and histamines onto alkynes.

Transition-metal-free chemo- and stereoselective addition of 5-aminoindole (1a), tryptamine (1b), and histamine (1c) to alkynes 2a-s to synthesize the indolyl/imidazolyl enamines 3a-p, 5a-o, and 6a-e using superbasic solutions of alkali-metal hydroxides in DMSO is described. The addition of N-heterocycles onto alkynes takes places chemoselectively without affecting the 1° amino groups (aromatic and aliphatic) of 5-aminoindole, tryptamine, and histamine. The stereochemistry of the products was found to be dependent upon reaction time; an increase in reaction time leads to the formation of a mixture of E/Z isomers and the thermodynamically stable E addition product. The chemoselective addition of N-heterocycle 1a onto alkyne over thiophenol 7 and phenol 8 is supported by control experiments. Competitive experiments showed that 5-aminoindole was more reactive than tryptamine, and histamine was found to be the least reactive. The present methodology provides an efficient chemoselective method to synthesize a variety of (Z)-enamines of 5-aminoindole, tryptamine, and histamine without affecting the 1° amino group. The presence of the free amino group in enamines could be further used for synthetic elaboration, which proved to be highly advantageous for structural and biological activity assessments.

Polymethylhydrosiloxane derived palladium nanoparticles for chemo- and regioselective hydrogenation of aliphatic and aromatic nitro compounds in water

Chemo- and regioselective hydrogenation of a wide range of aliphatic, unsaturated, aromatic and heteroaromatic nitro compounds into their corresponding amines has been achieved with highly efficient polysiloxane-stabilised “Pd” nanoparticles on NAP-magnesium oxide supports using an environmentally friendly hydrogenating agent, polymethylhydrosiloxane [PMHS] in water. Highly stable and active Pd nanoparticles were prepared by the reduction of NAP-Mg-PdCl4 with PMHS, which serves as a reducing agent as well as a capping agent. The well-dispersed palladium nanoparticles on NAP-MgO catalysts also exhibit excellent regioselectivity in the hydrogenation of dinitrobenzenes to the corresponding nitroanilines. The catalyst has high durability against sintering during the hydrogenation reaction and can be reused with no loss in its activity.

Magnetically separable nano-copper catalyzed unprecedented stereoselective synthesis of E-vinyl sulfones from tosylmethyl isocyanide and alkynes: TosMIC as a source of the sulfonyl group

We have developed an unprecedented efficient and mild catalytic route for stereoselective synthesis of E-vinyl sulfones from terminal alkynes and tosylmethyl isocyanide (TosMIC) in the presence of magnetically separable nano-copper (0) stabilized on Fe3O4. A variety of vinyl sulfones were obtained in moderate to good yields. In this newly developed protocol TosMIC acts as a sulfonyl source. The catalyst was magnetically removed and recycled easily five times without any appreciable loss in activity.

Transition-Metal-Free Quinoline Synthesis from Acetophenones and Anthranils via Sequential One-Carbon Homologation/Conjugate Addition/Annulation Cascade

A transition-metal-free method for the construction of functionalized quinolines from readily available acetophenones and anthranils is reported. This one-pot reaction cascade involves in situ generation of α,β-unsaturated ketones from the acetophenone via one-carbon homologation by DMSO followed by the aza-Michael addition of anthranils and subsequent annulation. DMSO acted in this reaction not only as solvent but also as one carbon source, thus providing a highly atom-economical and environmentally benign approach for the synthesis of 3-substituted quinolines.

Nanocrystalline magnesium oxide-stabilized palladium(0): an efficient and reusable catalyst for synthesis of N-(2-pyridyl)indoles

A selective and efficient catalytic process has been developed for the oxidative coupling between N-aryl-2-aminopyridines and alkynes using a nanocrystalline magnesium oxide (NAP–MgO)-supported palladium nanoparticle [NAP–Mg–Pd(0)] catalyst and CuCl2 as an oxidant. The process involves the ortho C–H activation of N-aryl-2-aminopyridines to give N-pyridyl indoles in excellent yields and the true heterogeneity of the catalyst is verified by studying the recoverability and reusability for four cycles without significant loss of catalytic activity.