Ramakanth Pagadala

Microwave assisted synthesis and characterization of N,N′-bis(salicylaldehydo)ethylenediimine complexes of Mn(II), Co(II), Ni(II), and Zn(II)

Microwave chemistry is a green chemical method that improves reaction conditions and product yields while reducing solvent amounts and reaction times. The main aim of this article is to synthesize the tetradentate N2O2 ligand [HO(Ar)CH=N–(CH2)2–N=CH(Ar)OH] and manganese(II), cobalt(II), nickel(II), and zinc(II) complexes of the type ML by classical and microwave techniques. The resulting Schiff base and its complexes are characterized by 1H NMR, infrared, elemental analysis, and electronic spectral data. The ligand and its Co(II) and Mn(II) complexes were further identified by X-ray diffraction and mass spectra to confirm the structure. The results suggest that the metal is bonded to the ligand through the phenolic oxygen and the imino nitrogen.

Eco-efficient ultrasonic responsive synthesis of pyrimidines/pyridines.

Using ultrasound irradiation, two simple one-pot multicomponent methods are described for syntheses of highly functionalized pyrimidine/pyridine derivatives in excellent yields in the presence of NaOH at room temperature. While one route involved aromatic aldehyde, thiourea and acetoacetanilide, the other employed aromatic aldehyde, malononitrile and benzyl mercaptane or EtOH. These approaches afford several advantages over former and contemporary reaction methodologies in terms of operational simplicity, simple work-up procedure, higher yield, short reaction time and environment friendly protocols.

Ultrasonic-accelerated rapid protocol for the improved synthesis of pyrazoles.

A simple, catalyst-free, green synthetic protocol is described for the one-pot synthesis of pyrazoles via multicomponent reaction of aromatic aldehydes, hydrazine monohydrate and ethyl acetoacetate and malononitrile/ammonium acetate in water under ultrasound irradiation. This protocol avoids traditional chromatography and purification steps and it affords highly selective conversion with no byproducts.

Mg–V/CO3 hydrotalcite: an efficient and reusable catalyst for one-pot synthesis of multisubstituted pyridines

Mg–V/CO3 hydrotalicite (Mg–V/CO3 HTlc) as an effective heterogeneous catalyst was synthesized by a simple technique. The catalyst was identified by PXRD, TEM, SEM and BET surface area analysis. The catalyst is fully recyclable and reusable for several runs preserving its high activity. The catalytic activity of Mg–V/CO3 HTlc is described by synthesis of a series of pyridines in good to excellent yields via a facile one-pot multicomponent reaction with a shorter reaction time.Graphical Abstract

Ce–Zr/SiO2: a versatile reusable heterogeneous catalyst for three-component synthesis and solvent free oxidation of benzyl alcohol

Ce–Zr loaded on SiO2 as catalyst provides an extremely efficient method to synthesize pyranoquinolines. This catalyst is found to be superb for the three-component synthesis of target compounds and for the solvent-free liquid-phase oxidation of benzyl alcohols. The catalyst is fully recoverable and reusable with no loss of catalytic activity even after multiple cycles.

Multicomponent synthesis of pyridines via diamine functionalized mesoporous ZrO2 domino intramolecular tandem Michael type addition

A new and straightforward synthetic method was developed for the facile synthesis of heterocycle-fused pyridine derivatives in aqueous media from Knoevenagel condensation between an aromatic aldehyde and an active methylene compound. This was followed by Michael type addition of a ketone to the activated double bond of the arylidene via intramolecular cyclization in the presence of diamine functionalized [N-(2 amino ethyl)-3-amino propyl trimethoxy silane (AAPTMS)] mesoporous ZrO2 (AAPTMS/m-ZrO2) to synthesize fused pyridines in high yield. This one-pot conversion, which involves multiple steps and requires no toxic/organic solvents, produced new C–C and C–heteroatom bonds with all reactants efficiently utilized.

Ultrasonic-mediated catalyst-free rapid protocol for the multicomponent synthesis of dihydroquinoline derivatives in aqueous media

Catalyst-free multicomponent protocol for the condensation of malononitrile, 2-naphthol/resorcinol, aldehydes, and ammonium acetate in aqueous medium under ultrasound irradiation at 60oC afforded a wide range of valuable dihydroquinolines in high yields (90–97%) with short reaction times (60–90 min). This approach offers vital improvements for the synthesis of target compounds with regard to yield of products, simplicity in operation, utilization of water as solvent, and green aspects by avoiding the catalysts or solvents.

Mild and Efficient Synthesis of Polyfunctionalized 4H-Pyran-3-carboxamide Derivatives

Simple and green synthetic approaches to valuable six-membered oxygen heterocyclic compounds are significant challenges in organic chemistry. Over the years, many attempts have been made to develop multi-component reactions for the synthesis of 4H-pyrans.1–8 4HPyran derivatives constitute a promising and versatile class of heterocycles with wide scope as natural and synthetic biologically active compounds,9–11 viz., anti-cancer agents, antianaphylactics, and anti-coagulants.12 A literature search indicates that amide-containing 4H-pyrans exhibit useful biological activities13 and a number of 2-amino-4H-pyrans are valuable photo-active materials.14 Most of the synthetic methods15–20 require expensive reagents, acidic conditions, long reaction times, excess of reagents or toxic organic solvents, and tedious work-up and in many of the methods, the yields are not impressive. Radiative and non-radiative techniques, such as microwave and ultrasonic irradiation have also been used.21,22 The present communication describes an environment-friendly method for the preparation of 4H-pyrans in good yields under mild conditions using water as a solvent. To our knowledge, there are no similar reports in the literature on the synthesis of tetra-substituted 4H-pyrans. The optimal conditions for synthesis of 4H-pyrans were determined to be K2CO3 as catalyst using one equiv. of acetoacetanilide (1), benzaldehyde (2a), and malononitrile 3 at room temperature (Scheme 1). The procedure was extended to a range of substituted benzaldehydes. All the compounds synthesized were characterized using IR, 1H NMR, 13CNMR, correct combustion analysis, and mass spectra. Compound 4a was further identified by 15N NMR (GHSQC) to confirm the presence of the amino group. All the 4H-pyran-3carboxamide derivatives were obtained in excellent yields (85%–98%).

Silver(I)–N-heterocyclic carbene catalyzed multicomponent reactions: a facile synthesis of multisubstituted pyridines

A four component one-pot reaction between aromatic aldehyde, malononitrile, ammonium acetate and ketone mediated by Ag(I) N-heterocyclic carbene to produce multisubstituted and fused pyridines in a short reaction time (∼10 min) in ethanol at room temperature is described.

Prediction of theoretical physicochemical properties and one-pot synthesis of bis-azetidinones by [2+2] ketene--imine cycloaddition in the presence of montmorillonite.

A simple, highly efficient and environmentally friendly microwave accelerated one-pot synthesis of a series of differently substituted bis-azetidinones have been synthesized expeditiously in good yields from 1,2-diaminoethane and aromatic aldehydes in the presence of zeolite. The structures of the newly synthesized compounds were confirmed by IR, NMR, and mass spectra. The design and calculated molecular properties of all the reported compounds are on the basis of hypothetical antibacterial pharmacophores, which were formulated to interact with microorganisms. A correlation of structure and activity relationship of these compounds with respect to Lipinski rules and drug likeness properties of drugs are described and verified experimentally.