Browsing by Author "Ashok Kumar Basak"

Now showing 1 - 4 of 4

Formal [4+1] heteroannulative coupling of Knoevenagel adducts derived from 2-heteroaryl acetonitriles with isocyanides: subsequent Pd-catalyzed intramolecular N-arylation to 6-5-5-5-6 pentacyclic cores
(Royal Society of Chemistry, 2023) Anamika Prajapati; Manoj Kumar Saini; Shashi Kant Verma; Harshita Singh Korawat; Ashok Kumar Basak
A concise and practical approach for expedient synthesis of substituted benzoxazolpyrroles, benzothiazolpyrroles and indolizines by three-component cascade annulative coupling of an aldehyde, 2-heteroaryl acetonitrile and an isocyanide in the presence of 10 mol% 2-(hydroxymethyl)pyrrolidinium acetate has been devised in high yields for the first time. The compatibility with a wide range of functional groups makes this domino formation of one C-C and two C-N bonds interesting. In particular, the heterocycles derived from 2-bromobenzaldehydes are further converted into indole-fused novel pentacyclic (6-5-5-5-6) heteroaromatic compounds by Pd(ii)-catalyzed intramolecular N-arylation via a cross-dehydrobromination reaction. This annulative protocol not only provides an efficient method to access tricyclic heteroaromatics, but also enriches the research domain of pentacyclic scaffolds. © 2023 The Royal Society of Chemistry.
Mitsunobu reaction of 1,3-dicarbonyl compounds and subsequent Pd-catalyzed intramolecular arylation: An expedient route to tricyclic oxoisochromenes
(Elsevier Ltd, 2025) Harshita Singh Korawat; Karmdeo Prajapati; Ashok Kumar Basak
1,3-Dicarbonyl compounds undergo chemoselective O-alkylation with (2-bromoaryl)methanols under Mitsunobu conditions at ambient temperature generating corresponding vinyl ethers in high yields. These vinyl ethers can be subsequently converted into tricyclic oxoisochromenes via previously reported ligand-free Pd-catalyzed intramolecular arylation reaction. © 2025 Elsevier Ltd
Novel oxoisochromene synthesis via chemoselective O-H insertion of 1,3-dicarbonyl compounds and subsequent Pd-catalyzed intramolecular arylation reaction
(Royal Society of Chemistry, 2023) Harshita Singh Korawat; Manoj Kumar Saini; Karmdeo Prajapati; Ashok Kumar Basak
Chemoselective O-alkylation of 1,3-diketones is a formidable synthetic challenge due to the competing C-alkylation reaction. In this report, N-triftosylhydrazones derived from 2-bromo(hetero)arylaldehydes are utilized for the O-alkylation of cyclic 1,3-diketones under base-mediated transition-metal-free conditions to generate vinyl ethers in good to high yields. The key to the success of the highly chemoselective O-alkylation reaction is the use of potassium enolate of 1,3-diketones as the base as well as the nucleophile in a highly polar-aprotic solvent at moderate temperature. These vinyl ethers are subsequently converted into novel oxoisochromene derivatives via Pd-catalyzed intramolecular arylation reaction. A plausible mechanism of the chemoselective O-alkylation reaction is outlined. © 2023 The Royal Society of Chemistry.
One-Pot Expeditious Synthesis of Pyrazoloindolones via Base-Promoted Electrocyclization, C–N Coupling and Intramolecular Oxidative Cyclization
(Georg Thieme Verlag, 2024) Harshita Singh Korawat; Manoj Kumar Saini; Karmdeo Prajapati; Maya Shankar Singh; Ashok Kumar Basak
Pyrazoloindolones are synthesized from N-tosylhydrazones in a one-pot multistep process which include base-promoted (i) electrocyclization reaction of N-tosylhydrazones derived from α,β-unsaturated aldehydes, (ii) aromatic nucleophilic substitution, and (iii) a domino cyclization–oxidation process under aerobic conditions. © 2024. Thieme. All rights reserved.