Novel One-Pot Multicomponent Strategy for the Synthesis of Pyrrolo[1,2-a]benzimidazole and Pyrrolo[1,2-a]quinoxaline Derivatives

Abstract

A simple one-pot multicomponent procedure has been developed for the synthesis of pyrrolo[1,2-a]benzimidazole and pyrrolo[1,2-a]quinoxaline derivatives by heating a 1:2:1 molar mixture of a benzimidazole unsubstituted on the imidazole ring, a 2-bromoacetophenone derivative, and a nonsymmetrical activated alkyne in refluxing 2-ethyloxirane. The reaction can be performed under conventional reflux conditions or with microwave irradiation.

The Cycloaddition of the Benzimidazolium Ylides with Alkynes: New Mechanistic Insights

“…A few decades later, Zhang and Huang [ 9 , 10 ] isolated a pyrrolo[1,2-a]quinoxaline instead of the expected pyrrolo[1,2-a]benzimidazoles, the mechanism proposed to explain the finding involving a concerted ring expansion, and hence no intermediates. Recent highlights [ 11 , 16 , 17 ] show that, depending on the substituents and/or the conditions employed, the reaction may be tuned toward the formation of either pyrrolo[1,2-a]benzimidazoles, pyrrolo[1,2-a]quinoxalin-4-ones [ 16 ] or pyrrolo[1,2-a]quinoxalines [ 11 ]. The mechanism proposed involves aromatization of the pyrrole ring concomitant with the opening of imidazole ring leading to 2-pyrrolo-aniline intermediates.…”

Iron-Catalyzed Intramolecular C(sp2)–N Cyclization of 1-(N-Arylpyrrol-2-yl)ethanone O-Acetyl Oximes toward Pyrrolo[1,2-a]quinoxaline Derivatives

“…The product was isolated by flash chromatography (eluent EtOAc:PE = 1:10) as a yellow oil (437 mg, 79%): 1 H NMR (400 MHz, CDCl 3 ) δ 7.38 (d,J = 8.4 Hz,2H),7.23 (d,J = 8.4 Hz, 2H), 6.87 (t, J = 1.6 Hz, 1H), 6.72 (dd, J = 3.6, 1.2 Hz, 1H), 6.31 (t, J = 3.4 Hz, 1H), 2.19 (s, 3H), 1.87 (s, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ) δ 170. 4,154.6,139.8,133.0,129.0,128.2,127.3,127.2,116.0,109.6,19.4,15.2;HRMS (ESI), m/z calcd.…”

“…for C 15 H 13 F 3 N 2 O 2 ([M + Na] + ) 333.0821, found 333.0826; IR (KBr, neat) v 3062, 1771(KBr, neat) v 3062, , 1653(KBr, neat) v 3062, , 1599(KBr, neat) v 3062, , 1498(KBr, neat) v 3062, , 1364(KBr, neat) v 3062, , 1196(KBr, neat) v 3062, , 1098. (d,J = 7.6 Hz,1H),7.57 (d,J = 2.0 Hz,1H),7.54 (d,J = 8.0 Hz,1H),7.49 (d,J = 7.6 Hz,1H),6.91 (dd,J = 2.8,1.6 Hz,1H), 6.76 (dd, J = 3.6, 1.6 Hz, 1H), 6.35 (dd, J = 3.6, 2.8 Hz, 1H), 2.25 (s, 3H), 1.78 (s, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ) δ 170. 3,154.1,141.9,131.6,131.2,129.6,129.5,128.4,127.3,124.9,124.0 (q,J = 3.7 Hz),123.2(q,J = 3.7 Hz),116.5,110.0,19.3,14.9; HRMS (ESI), m/z calcd.…”

“…(E)-1-(1-(4-Methoxyphenyl)-1H-pyrrol-2-yl)ethan-1-one Oacetyl oxime (1b). The product was isolated by flash chromatography (eluent EtOAc:PE = 1:12) as a white solid (425 mg, 78%): mp 58−60°C; 1 H NMR (400 MHz, CDCl 3 ) δ 7.21 (d, J = 8.8 Hz, 2H), 6.92(d, J = 8.8 Hz, 2H), 6.87 (t, J = 1.6 Hz, 1H), 6.69 (dd, J = 3.6, 1.6…”

“…H NMR (400 MHz, CDCl 3 ) δ 8.07(d, J = 8.4 Hz, 2H), 7.32 (d, J = 8.4 Hz, 2H), 6.91 (dd, J = 2.8, 2.0 Hz, 1H), 6.72 (dd, J = 4.0, 1.6 Hz, 1H), 6.31 (t, J = 3.4 Hz, 1H), 4.36 (q, J = 7.2 Hz, 2H), 2.16 (s, 3H), 1.81 (s, 3H), 1.38 (t, J = 7.2 Hz, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ) δ 170.2, 165.6, 154.6, 144.7, 130.3, 128.9, 127.8, 127.1, 125.3, 116.3, The Journal of Organic Chemistry Note 109.9, 61.0, 19.4, 15.3, 14.1; HRMS (ESI), m/z calcd. for C 17 H 18 N 2 O 4 ([M + Na] + ) 337.1159, found 337.1179; IR (KBr, neat) v 3116,…”