L. Raju Chowhan

Asymmetric Mannich reaction: highly enantioselective synthesis of 3-amino-oxindoles via chiral squaramide based H-bond donor catalysis

We describe here a simple and facile asymmetric Mannich reaction catalyzed by chiral Cinchona alkaloid based squaramide containing H-bond donor catalysts, wherein, the reaction of 1,3-diketones with isatin (N-Boc) ketimines led to the formation of 3-aminooxindole derivatives. These derivatives were obtained in high yields with excellent enantioselectivities under mild conditions using 3 mol% of the catalyst. This protocol provides valuable and easy access to chiral 3-substituted 3-aminooxindole derivatives.

Hydrophobically directed, catalyst-free, multi-component synthesis of functionalized 3,4-dihydroquinazolin-2(1H)-ones

A one-pot three-component reaction of o-formyl carbamate, a primary amine, a nucleophile (1H-indole or 2-napthol) in water generated a variety of functionalised 3,4-dihydroquinazolin-2(1H)-one derivatives. The reaction operated under catalyst-free conditions involves a Mannich type reaction followed by intramolecular cyclization and produced good to excellent yields of the products with a wide range of substrates. The environmentally benign multi-component reaction is a sustainable approach to the library of 3,4-dihydroquinazolin-2(1H)-one derivatives under completely neutral conditions. All the newly synthesized compounds were evaluated for their antimicrobial activity against Gram positive bacteria and Gram negative bacteria. Nineteen compounds exhibited good antibacterial activity against both Gram positive pathogens and Gram negative species.

Silver(I) catalyzed intramolecular cyclization of N-(2-(alk-1-yn-1-yl))-1H-tetrazoles leading to the formation of N-cyano-2-substituted indoles under ambient conditions

A facile silver(I) catalyzed intramolecular cyclization reaction of alkynyl tetrazoles to form N-cyano-2-substituted indoles has been investigated. This unique cyclization involves the formation of a C–N bond during the intramolecular cyclization of N-(2-(alk-1-yn-1-yl))-1H-tetrazoles in the presence of silver(I) acetate. Good to excellent yields were obtained using low catalyst loadings, ∼5 mol%, under mild conditions.

Exploring TiO2 NPs as efficient catalyst for 1,6 Michael addition of 3-methyl-5-pyrazolone on 3-methyl-4-nitro-5-alkenyl isoxazoles and rapid synthesis of 3,3‐bis(indolyl)oxindoles in water

Abstract We here present a report on development of a column chromatography free, heterogenous titanium dioxide nanoparticles (TiO2 NPs) catalyzed 1, 6 Michael addition of 3-methyl-5-pyrazolone on 3-methyl-4-nitro-5-alkenyl isoxazoles and rapid synthesis of 3,3-di(indolyl)indolin-2-ones by reaction of indole on isatin at room temperature in water for the first time. Moderate to good yield was obtained in case of 1, 6 Michael addition reaction and quantitative yield in case of a 3,3‐bis(indolyl)oxindole products. A scale up experiment on gram scale was performed successfully for both the reactions. Recyclability experiment was carried out for 4 cycles and turn over frequency (TOF) calculation for each cycle are presented for both reactions, which clearly indicate the sustainability of the protocol. In addition, green chemistry matrices (atom economy, reaction mass efficiency (RME), E-factor, process mass intensity (PMI)) values suggest that the presented methodology is green and eco-friendly. Graphical Abstract

Aqueous single step synthesis and structural characterization of allylated, propargylated, and benzylated 3-substituted 3-aminooxindoles

ABSTRACT Efficient zinc-mediated allylation, propargylation, and benzylation of isatin-derived imines were undertaken for the synthesis of 3-substituted 3-aminooxindoles with ≈80% yield. Such alternative approach has efficiently avoided the use of catalysts, severe reaction conditions, multistep procedures, and reaction additives. For exploring and materializing the synthetic utility, different allyl, propargyl, and benzyl bromides were used for generalizing the synthetic route. The structure of the synthesized compounds was established and confirmed by 1H NMR, 13C NMR, FTIR, and mass spectroscopic techniques. GRAPHICAL ABSTRACT