Multicomponent Synthesis of Fluorescent Thiazole–Indole Hybrids and Thiazole-Based Novel Polymers

Abstract

Herein, we report an efficient multicomponent reaction for the synthesis of trisubstituted thiazoles involving a one-pot C–C, C–N, and C–S bond-forming process from the readily available starting materials. The reaction of arylglyoxal, indole, and aryl thioamides in the acetic acid medium under sealed heating conditions provided 3-(2,4-diarylthiazol-5-yl)-1H-indoles (4) in good to excellent yields. Using a similar reaction strategy, the reaction of arylglyoxal, aryl thioamide, and 2,5-dihydroxy-1,4-benzoquinone provided structurally interesting bis-thiazoles having dihydroxy-1,4-benzoquinone linker (9). All of the products were fully characterized by spectroscopic techniques. We also recorded single-crystal X-ray diffraction (XRD) of compounds 4b and 9a for unambiguous structure determination. Indole-linked trisubstituted thiazoles (4) exhibit prominent fluorescence properties. The relative fluorescence quantum yields of all of the thiazole-linked indoles were measured in the dimethyl sulfoxide (DMSO) medium with respect to quinine sulfate in 0.1 M H2SO4 as reference. The scope of this reaction was further explored by preparing novel polymers 11a and 11b using naphthalene/benzene-1,4-bis­(carbothioamide) in multicomponent polymerization.

Humic Acid: A Promising and Green Bioorganic Catalyst in Organic Syntheses

“…The 1,3-dicarbonyls, [30] indoles [31] are popular precursors in MCRs. In this backdrop, Mitra et al in 2021 reported the humic acid-catalyzed synthesis of a library of molecules under solventfree conditions as shown in Scheme 3.1, 3.2, 3.3 and 3.4.…”

Iodine-Promoted Thioylation and Dicarbonylation of Enaminone α-C Sites: Synthesis of Fully Substituted Thiazoles via C═C Bond Cleavage

“…Over the past few decades, the preparation of polysubstituted thiazole skeletons has become particularly interesting, as such skeletons are particularly important N- and S-containing heterocycles with good pharmacological profiles and extensive biological activities . Nevertheless, direct de novo synthesis of fully substituted thiazoles with dicarbonyl functional groups from easily available materials remains challenging, because it is difficult to synthesize heterocycles in situ while achieving their carbonylation in one reaction.…”

HFIP-Mediated Multicomponent Reactions: Synthesis of Pyrazole-Linked Thiazole Derivatives

“…Conventionally thiazoles are prepared by Hantzsch thiazole synthesis involving α-halo ketone and thioamides . Considering the importance of green chemistry and the requirement for better alternative methods for the synthesis of substituted thiazoles, over the years, many methods have been developed using the combinations of different starting materials as well as catalysts and reaction conditions . Comparison of a few recent methods with our present method for the synthesis of substituted thiazoles is shown in Scheme .…”