Pranjal K. Baruah

Self-complementary quadruple hydrogen bonding motifs: from design to function

Self-assembly is an important phenomenon that allows nature to carry out many important functions. Of the several non-covalent interactions present H-bonding finds a special place in the design strategies employed by chemists due to its specificity and directional nature. The strength, directionality, and specificity of H-bonding interactions could be further enhanced by using a combination of several such interactions. This review discusses exclusively the developments in the field of self-complementary quadruple H-bonded motifs and their application in various emerging fields.

Sheet-forming abiotic hetero foldamers

Abiotic hetero oligomers, adopting a well-defined extended self-assembled sheet-like structure, derived from conformationally constrained aliphatic and aromatic amino acid residues repeating at regular intervals are reported.

Copper catalyzed oxidative deamination of Betti bases: an efficient approach for benzoylation/formylation of naphthols and phenols

An efficient route for benzoylation or formylation of naphthols/phenols is developed via oxidative deamination of Betti bases. A copper salt catalyst with TBHP as an oxidant is used. Water is used as a reagent as well as solvent. The reaction proceeds through a regioselective radical pathway. Most importantly, the position of acylation is unambiguous. The method is also applicable to non-hydroxy substrates.

Copper oxide nanoparticle mediated ‘click chemistry’ for the synthesis of mono-, bis- and tris-triazole derivatives from 10,10-dipropargyl-9-anthrone as a key building block

The synthesis of mono-, bis- and tris-triazole derivatives was accomplished using 10,10-dipropargyl-9-anthrone as a key starting material. Various acetylenic compounds (2–5) derived from 10,10-dipropargyl-9-anthrone on reaction with alkyl/benzyl bromides and sodium azide in the presence of 10 mol% of copper oxide nanoparticles along with 20 mol% sodium ascorbate in water afforded a wide variety of triazoles derivatives (8–13) under heating at 70 °C. The salient features of the present protocol are: mild reaction conditions, a shorter reaction time, the reusability of the catalyst, and its applicability with a wide range of substrates. Moreover, the mono-triazole 8b undergoes extended assembly in the solid state forming a zig-zag supramolecular structure stabilized by π–π and C–H⋯π interactions. Interestingly, the single crystal X-ray structure of 9b shows that it forms a supramolecular ball structure stabilized by a combination of C–H⋯O interaction and hydrogen bonding. Furthermore the presence of water molecules embedded in the crystal lattice of 9b allows these supramolecular balls to arrange in a chain generating a fascinating supramolecular architecture.

Catalyst-free multi-component cascade C–H-functionalization in water using molecular oxygen: an approach to 1,3-oxazines

Herein, catalyst-free 3-component reactions of naphthols, aldehydes, and tetrahydroisoquinolines to synthesize 1,3-oxazines is reported. The reaction is performed in H2O in the presence of O2 as the sole oxidant at 100 °C, which proceeds through the formation of 1-aminoalkyl-2-naphthols followed by selective α-C–H functionalization of tert-amine.

C-C Bond Cleavage: Metal-Free-Catalyzed Reaction of Betti Bases with Various Heterocycles Under Microwave Irradiation

ABSTRACT The reaction of Betti bases with various heterocycles in the presence of p-toluenesulphonic acid (PTSA) under microwave irradiation gives bis(heterocycle)methanes through benzyl transfer. The reaction proceeds via the cleavage of C-N bond followed by C-C bond. The metal-free cleavage of C-C bond, which is in fact a C-dearylation, is rarely reported in the literature. GRAPHICAL ABSTRACT

The solid-state behaviour of 4,6-dioxo-5,5-diethylenepyrimidine-2-isobutylurea

The solid-state behaviour of 4,6-dioxo-5,5-diethylenepyrimidine-2-isobutylurea (PIBU) has been investigated. Two polymorphic forms have been identified, a monoclinic α form and a triclinic γ form, both of which undergo a destructive phase transition below 165 K. The α form undergoes an additional temperature-dependent phase transition at approximately 250 K to give the β form. All three forms of PIBU have been structurally characterised by X-ray diffraction. In all three crystal structures the PIBU molecules are organised into dimer units, which are stabilised by a self-complementary AADD quadruple hydrogen bond array.

CAN-catalyzed microwave promoted reaction of indole with Betti bases under solvent-free condition and evaluation of antibacterial activity of the products

ABSTRACT CAN-catalyzed reaction of Betti bases with indoles under microwave irradiation gives 3-(α,α-diarylmethyl)indoles. Better yield of the products, especially when one of the aryl ring is phenol were achieved. The reaction is performed in solvent-free condition. The antibacterial studies of the synthesized compounds were performed and some of the compounds showed good activity against Methicillin-resistant Staphylococcus aureus bacteria. GRAPHICAL ABSTRACT

One-pot sequential multi-component reaction: Synthesis of 3-substituted indoles

Abstract Here, we have developed a 3-component one-pot sequential approach to 3-substituted indoles. The main advantages of this process are step economy, reduced waste, and operational simplicity. The method involves in situ generation of 3-indolylalcohols from the reaction of indoles and aldehydes in the presence of base. Further, nucleophilic substitution of 3-indolylalcohols with various nucleophiles affords 3-substituted indole derivatives. The reaction does not requires any hazardous and expensive metal catalyst. In addition, the reaction is carried out in (1:1) ethanol–water which is considered as environmentally benign solvent. On the other hand, nonsequential 3-component reaction results in the formation of unwanted bisindolylmethanes. Graphical Abstract

A revisit to the multi-component reaction of indole, aldehyde, and N-substituted aniline catalyzed by PMA–SiO2

PMA–SiO2-catalyzed multi-component reaction of indole, aromatic aldehyde, and N-substituted aniline at room temperature under solvent-free condition is reported here. The reaction was previously reported, where a C–C and C–N bond were formed. However, we established a different structure for the product with the help of NMR as well as single-crystal X-ray studies, where the C-4 atom of N-substituted aniline is linked to the aldehydic carbon, and consequently, two new C–C bonds are formed. The mechanism of the reaction is established through trapping of the intermediate which is also different from the previous report. To the best of our knowledge, only one report is available in the literature for the synthesis of this class of important compounds.Graphical abstract