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)-1<i>H</i>-indoles (<b>4</b>) 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 (<b>9</b>). All of the products were fully characterized by spectroscopic techniques. We also recorded single-crystal X-ray diffraction (XRD) of compounds <b>4b</b> and <b>9a</b> for unambiguous structure determination. Indole-linked trisubstituted thiazoles (<b>4</b>) 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 <b>11a</b> and <b>11b</b> using naphthalene/benzene-1,4-bis(carbothioamide) in multicomponent polymerization.