A wide variety of 2-substituted benzimidazoles and bis-benzimidazoles were synthesized in high yields by PEG-mediated catalyst-free synthesis under solvent-less conditions. The products were directly recrystallized from hot methanol. The reaction occurred giving excellent yields with low as well as high molecular weight PEGs. © 2008 Elsevier Ltd. All rights reserved.

CHHANDA MUKHOPADHYAY

Chemistry

P K TAPASWI

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

&nbsp;

The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

&nbsp;

It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Tetrahedron Letters

Potassium hydrogen sulfate in the presence of dibenzo-18-crown-6 (DB18C6) turns out to be a very efficient and effective catalyst for the facile synthesis of a wide variety of tri- and tetrasubstituted imidazoles in an aqueous medium at moderate temperature. The idea behind this is that the potassium ion, being trapped in the crown core, frees the hydrogen sulfate anion, which, because of its acidic nature, succeeds in the ready synthesis of the imidazoles. © 2012 Copyright Taylor and Francis Group, LLC.

Fulltext

Green Chemistry Letters and Reviews

A facile and efficient synthesis of tri- and tetrasubstituted imidazoles with potassium hydrogen sulfate and DB18C6 in an aqueous medium

Only 15 mol% of l-proline in ethanol proved to be a very efficient catalyst for the one-pot synthesis of a wide variety of highly substituted pyridines at room temperature. The methodology is mild, efficient, high yielding, and the products can be directly recrystallized from hot ethanol. © 2010 Elsevier Ltd. All rights reserved.

l-Proline-catalyzed one-pot expeditious synthesis of highly substituted pyridines at room temperature

Three component coupling of an aromatic dialdehyde, a β-keto ester or β-diketone and urea or thiourea (1:2.2:2.5 mol ratios) in one-pot under solvent-free conditions without any catalyst produced the bis-dihydropyrimidones (thiones) in a microwave oven. This is therefore a "green" synthesis of the title compounds under the said conditions. © 2010.

Heterocycles

A non-catalyst method for the synthesis of bis-4-aryl-3,4-dihydropyrimidones (thiones) under solvent-free conditions

A very simple, mild, and highly efficient green catalyst has been developed for the synthesis of 2-substituted benzimidazoles by treatment of substituted ortho-phenylenediamines and aldehydes in water at 80C in the presence of boric acid (5 mol-%) and glycerol (0.05 mL). This methodology has been standardized on 55 substrates, and nine new compounds have been synthesized. © 2009 CSIRO.

Australian Journal of Chemistry

Water-mediated synthesis of 2-substituted benzimidazoles by boric acid and glycerol

A facile and efficient method for the preparation of 3,4,6,7-tetrahydro-9- (1,2-dihydro-2-oxoquinolin-3-yl)-2H-xanthene-1,8(5H,9H)-diones from substituted 2-chloro-3-formylquinoline and 1,3-cyclohexanedione or dimedone in water at 90 °C using parallel synthesizer is reported. The present methodology offers a tandem-cascade methodology, high yield, and operational simplicity. © 2014 Elsevier Ltd. All rights reserved.

Water mediated catalyst-free efficient domino synthesis of 9-(quinolin-2(1H)-one)-xanthene-1,8(5H,9H)-diones using parallel synthesizer

Aromatic aldehydes with both electron withdrawing and electron donating substituents were smoothly converted to the corresponding 2-arylbenzothiazoles by direct condensation of aromatic aldehydes with 2-aminothiophenol in one pot in a microoven under solvent-free conditions without any catalyst. The study revealed that the synthesis proceeded in three stages; first the formation of the aryl imine followed by its cyclisation to the benzothiazoline which in turn underwent oxidation and dehydration to the final product benzothiazole. Isolation of intermediates in all the stages confirmed the mechanism. This is therefore the first report of a "green" synthesis of the 2-arylbenzothiazoles under solvent-free conditions in the absence of any catalyst. © 2007 The Japan Institute of Heterocyclic Chemistry.

Journal	Data powered by TypesetTetrahedron Letters
Publisher	Data powered by TypesetPERGAMON-ELSEVIER SCIENCE LTD
ISSN	0040-4039
Open Access	No