Pyrrolo[1,2-a]quinoxalines: Novel Synthesis via Annulation of 2-Alkylquinoxalines

Abstract

In an attempt to synthesize a novel homoleptic complex 3 from 2-methyl-3-phenylquinoxaline 1 and Ir(acac)(3) for application as a triplet emitter in OLEDs (organic light-emitting diodes) no cyclometalation was observed. Instead, an annulation to 1-methyl-4-phenylpyrrolo[1,2-a]quinoxaline 2 was observed. Since pyrroloquinoxalines are potentially bioactive and few paths for their synthesis are known, selected reactions and conditions were investigated, suggesting Ir(acac)(3) as catalyst and proving glycerol to be a reactant.

HOAc-Mediated Cyclocondensation of 2-Formylazaarenes and Cyclic Amines. Synthesis of Pyrrolo[1,2-a]azaarenes

“…Melting points were obtained with an SMP3 melting apparatus. 1 H (400 MHz) and 13 C NMR (100 MHz) spectra were recorded on a Varian INOVA-400 spectrometer, respectively. Chemical shifts (δ) are reported in ppm, and the J values are given in hertz.…”

“…11-Quinolin-2-ylmethyl-8,9,10,11-tetrahydro-11,11bdiazabenzo [c] (m, 1H), 1.66−1.62 (m, 1H). 13 C{ 1 H} NMR (100 MHz, CDCl 3 ): δ 158.6, 147.5, 140.6, 140.4, 139.1, 136.9, 135.8, 135.4, 134.0, 129.6, 129.4, 128.9 (2×), 128.7 (2×), 127.7, 127.5, 127.4 (2×), 127.00, 126.96 (2×), 126.9, 125.7, 125.30, 125.28, 124.9, 120.5, 119.5, 117.5, 117.0, 112.9, 100.8, 58.2, 48.7, 21.9, 15.9.…”

“…Pyrrolo-fused azaarene is an important class of scaffolds in a wide range of bioactive molecules, synthetic intermediates and photochromic materials. − Due to its potential applications, the development of a one-pot synthetic route to access these motifs has attracted significant attention, and many development attempts have been reported. As shown in Scheme , the general approach toward pyrrolo­[1,2- a ]­azaarene core system 1 is based on a domino process by transition-metal (e.g., Rh 3+ , Pd 2+ , Cu + , Ir 3+ , Mo 4+ )-catalyzed annulation. − ,− ,, The cyclization reactions mediated by the metal-free reagents (e.g., Ph 2 PCl, I 2 , HOAc) require a synthetic route for constructing this core skeleton. ,,, Organocatalyst-promoting pioneering methods have been explored as a unique strategy …”

“…As shown in Scheme 1, the general approach toward pyrrolo[1,2-a]azaarene core system 1 is based on a domino process by transition-metal (e.g., Rh 3+ , Pd 2+ , Cu + , Ir 3+ , Mo 4+ )-catalyzed annulation. [4][5][6][9][10][11]13,15 The cyclization reactions mediated by the metal-free reagents (e.g., Ph 2 PCl, I 2 , HOAc) require a synthetic route for constructing this core skeleton. 7,8,12,14 Organocatalyst-promoting pioneering methods have been explored as a unique strategy.…”

Tandem 6π-Azatriene Electrocyclization of Fused Amino-cyclopentenones: Synthesis of Functionalized Pyrrolo- and Indolo-quinoxalines

“… − Furthermore, substituted pyrrolo­[1,2- a ]­quinoxaline derivatives possess many unique and excellent properties such as antitumor, , antileishmanial, antimalarial, anti-HIV, human protein kinase CK2 inhibition, D-loop activity of RAD51 inhibition, and adenosine A3 receptor modulation properties . Because of the significant importance of these compounds, many methods have been reported to construct the core. − Despite having notable advances, − the developed strategies still require advancement in terms of the substrate scope and metal-free and operational simplicity.…”