Microwave assisted one pot synthesis of 2-ethylamino benzimidazole, benzoxazole and benzothiazole derivatives

Abstract

Supporting InformationTable of Contents 1. General method and materials S2 2. Experimental procedure and analytical data of the products S3 3. Spectral data of the products S10 S2 General methods All reagents were obtained from Sigma-Aldrich Chemical Co and were used without further purification. All solvents were analytical grade. 1 H and 13 C NMR spectra were recorded on a Bruker AC 200 ( 1 H NMR, 400 MHz; 13 C NMR, 50.32 MHz). CDCl3 and DMSO-D6 were used as the solvent and tetramethylsilane as an internal standard. Chemical shifts are reported in δ (ppm). Abbreviations for NMR data are as follows: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, dd = doublet of doublets, dt = doublet of triplets, app = apparent, br = broad. High-resolution mass spectra (HRMS) were obtained on a Thermo IonTrap Mass Spectrometer equipped with an electrospray ion source (ESI), operated in the positive mode. Mass spectra were obtained using electrospray (ES) ionization techniques. All temperatures are reported in degrees centigrade. Reactions were routinely monitored by TLC using Merck silica gel F254 plates. Melting points were measured on a Büchi melting point apparatus and are uncorrected. The purity (> 98%) of commercial samples and final products was confirmed by TLC (Merck silica gel plates of type 60 F254, 0.25 mm layer thickness) and combustion analysis. Microwave irradiation was carried out using a Monowave Edu (Anton Paar) apparatus (200 W, 2 min, 1 bar). Flash column chromatography was performed over silica gel 100-200 mesh, and the solvents were distilled prior to use. DMSO was dried over 4 Å molecular sieves prior to use. S3General procedure for synthesis of N-ethyl -benzimidazole 2-amine by MW irradiation.A mixture of o-phenylenediamine (1.0 mmol) and EDC.HCl (1.1 mmol) in 2-propanol (10 mL) was irradiated in microwave apparatus at 200 W (80 °C) for 15 min. The reaction was monitored by TLC (eluent CH2Cl2 / MeOH 95:5). After completion, the reaction mixture was diluted with water (20 mL) and extracted with EtOAc (2 x 25 mL). The combined organic layers were washed with brine, dried over anhydrous Na2SO4 and concentrated under reduced pressure and the obtained crude product was purified by flash column chromatography using silica gel (100-200 mesh) with 1-5% MeOH/CH2Cl2 as eluent. The fractions containing product were collected and concentrated under reduced pressure to afford N-ethyl-1Hbenzo[d]imidazol-2-amine (1a, 90% yield) as an off white solid. N-Ethyl-1H-benzo[d]imidazol-2-amine (1a). 6(a)Off-white solid. IR (KBr)υmax: 3403, 3053,

Advances in the synthetic strategies of benzoxazoles using 2-aminophenol as a precursor: an up-to-date review

“…Ease of operation, good yield, and nontoxic and easily available reagents are the notable advantages of this method (Scheme 19; method 1). Rapolu et al 88 illustrated a facile simple one-pot reaction for the synthesis of benzoxazole derivatives (28) under microwave irradiation at 80 °C from 2-aminophenol (1) and EDC$HCl (27) in isopropanol. This pathway provided some merits like a onestep reaction, simple operation, shorter reaction time, and the use of MW irradiation (Scheme 19; method 2).…”

Recent achievements in the synthesis of benzimidazole derivatives

“…Rapolu et al described an efficient one-pot procedure for the preparation of 2-ethylamino benzimidazole from o -phenylenediamines with EDC·HCl. 174 The microwave-assisted synthesis gave products in high yields in a short reaction time. A reaction mechanism was also outlined ( Scheme 105 ).…”