Aromaticity as a Cornerstone of Heterocyclic Chemistry

Abstract

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Properties, environmental fate and biodegradation of carbazole

“…It can also be considered a manifestation of cyclic delocalization and resonance (Balaban et al 2004). The tendency to favor substitution rather than addition suggests that the parent unsaturated ring system has exceptional stability.…”

“…It has a molecular weight of 167.21 g/mol, boiling and melting point of 355 and 246°C (Lide 2003), water solubility of 1.2 mg/l (Johansen et al 1997), vapor pressure of 1 9 10 -4 Pa (Peddinghaus et al 2012), and octanol/water partition coefficient (log K ow ) of 3.72 (Blum et al 2011). It is one of the p-excessive heterocycles (electron-rich rings) and is more recalcitrant than dibenzofuran but less than dibenzothiophene (Balaban et al 2004). It is a white crystalline solid at ambient temperature.…”

Microwave-assisted synthesis of nitrogen-containing heterocycles

“…When the homogenous mixture of equal molar quantities of benzaldehyde 51, benzil 52, glacial acetic acid, and R = morpholine, pyrrolidine, piperidine, R' = aryl groups Wolkenberg et al [44] described a simple, highyielding (80-99%) synthesis of 2,4,5-trisubstituted imidazoles 57 from 1,2-diketones 56 and aldehydes 55 in the presence of NH 4 OAc under MW irradiation at 180˚C for 5 min (Scheme 17). Classical methods require harsh reaction conditions (150-200˚C, 4-6 h) and suffer from low yields (40-90%), mixtures of products, and lack of generality.…”

“…2,3-Dihydro-1H-pyrrolo[3,2-c]quinoline 179 (13 examples) core from substituted 2-iodoanilines 176 and 2,3-dihydro-1H-pyrrole 177 was achieved using 10 mol% Pd(PPh 3 ) 4 and K 2 CO 3 in 1,4-dioxane at 170˚C for 1 h in an MW oven in 60% yield (Scheme 51). But, the reaction of 176 and 177 in refluxing toluene for 24 h produces 179 in 44% [86].…”

“…Amongst the heterocycles, N-based heterocycles have been the object of considerable focus, because N-containing heterocycles are structural components of many bioactive natural products such as vitamins, hormones, antibiotics, alkaloids, glycosides, and many more compounds which are of significance for human and animal health [4]. Many natural drugs such as quinine, papaverine, emetine, theophylline, atropine, codeine, morphine, and reserpine are Ncontaining heterocycles [1,5].…”