Imidazo[1,2-a]benzimidazole derivatives: XXVIII. Syntheses and heterocyclizations on the basis of 1-allyl-2-aminobenzimidazole

Abstract

Addition of hydrogen bromide at the double bond of 1-allyl-2-amino-1H-benzimidazole and 3-alkyl-(benzyl)-1-allyl-2-amino-1H-benzimidazolium halides was studied. The resulting 1-(2-bromopropyl) derivatives were subjected to thermolysis under different conditions, and the structure of dehydrobromination products was determined and proved by independent synthesis via prototropic isomerization of the allyl group by the action of bases. * For communication XXVII, see [1].Allyl-substituted aromatic and heterocyclic compounds attract researchers' attention due to their high reactivity and the possibility for synthesizing fused heterocyclic systems on their basis. Intramolecular cyclizations of α-allyl-substituted hetarenethiones [2-4] and hetarenamines [5,6] were reported in a number of publications. Development of new methods for the synthesis of imidazo[1,2-a]benzimidazole derivatives from 1-allyl-2-aminobenzimidazole (I) is promising, taking into account broad spectrum of biological activity intrinsic to that tricyclic system [7][8][9][10][11].First of all, the procedure for the synthesis of amine I was optimized. N-Substituted 2-aminobenzimidazoles were commonly prepared by amination of

Imidazo[1,2-a]benzimidazole derivatives: XXIX. 1-allyl-2-amino-3-acylmethylbenzimidazolium halides and syntheses on their base

“…Quaternization of 1-(2-bromopropyl)-1H-benzimidazol-2-amine (X) [1] with phenacyl bromide in acetone gave salt XI which was found to undergo cyclization along two pathways, depending on the conditions. By heating bromide XI with excess 48% hydrobromic acid we obtained hydrobromide Vc (Scheme 3).…”

“…As shown in [1], 1-allyl-3-alkyl-(arylalkyl, dialkylaminoalkyl)-2-imino-2,3-dihydro-1H-benzimidazoles take up hydrogen bromide at the allyl group, and next follows heterocyclization with formation of 9-substituted 2-methyl-2,3-dihydroimidazo [1,2-a]benzimidazoles. Some cyclization products exhibited interesting biological properties [6].…”

“…Yield 3.6 g (97%), mp 242-244°C (from EtOH). IR spectrum, ν, cm -1 : 3200, 3150 (NH 2 ), 1690 (C=O), 1665, 1600, 1500, 1460 (C=C, C=N) 1. H NMR spectrum (DMSO-d 6 ), δ, ppm: 4.95 d (2H, CH 2 , 21.46; N 11.29.…”

“…Like 1-allyl-3-alkyl(arylalkyl)-2-aminobenzimidazolium salts [1], compounds IIa-IIc take up hydrogen bromide at the allyl group on heating in boiling concentrated hydrobromic acid; simultaneously, intramolecular cyclization with participation of the amino and carbonyl groups occurred to give tricyclic 2-R-9-(2-bromopropyl)imidazo[1,2-a]benzimidazoles Va-Vc [8]. The latter can also be obtained by heating 9-allyl derivatives IVa-IVc with concentrated hydrobromic acid.…”

“…Yield 94%, colorless oily substance. IR spectrum, ν, cm -1 : 1660, 1615, 1600, 1495, 1480 (C=N, C=C) 1. H NMR spectrum (CDCl 3 ), δ, ppm: 1.08 d (3H, CH 3 , J = 7.7 Hz), 2.40-2.53 m (2H, CH 2 ), 2.69-2.82 m (4H, NCH 2 ), 3.24-3.40 m (1H, CH), 3.44-3.61 m (4H, OCH 2 ), 4.01-4.13 m and 4.27-4.40 m (1H each, 9-CH 2 ), 7.10-7.44 m (6H, H arom ), 7.52 d (1H, H arom , J = 8.8 Hz), 7.62 s (1H, 3-H), 7.84 d (2H, 5-H, 8-H, J = 7.7 Hz).…”