Some reactions of 5‐methyl‐11H‐isoindolo[2,1‐α] benzimidazolium salts

Abstract

5‐Methyl‐11H‐isoindolo[2,1‐α]benzirnidazolium halide (IV), obtained by direct quaternization of the precursor III, underwent facile condensation reactions at its 11‐methylene group similar to those of 11H‐isoindolo[1,2‐b]benzothiazolium cation II. Although the treatment of II with alkali regenerated its precursor I, treatment of IV with alkali caused ring opening to a phthalimidine. Attempted thermal cyclization of 2‐(alkylaminophenyl)phthalimidines, e.g., VII, resulted in dealkylation to produce III.

11H-isoindolo[2,1-a]benzimidazoles (Review)

“…The imidazole ring of the 11H-isoindolo[2,1-a]benzimidazolium salt 55c is opened by the action of alkali with the formation of compound 60 [22,72]. In [72] it was noticed that a yellow crystalline substance, which may be 5-methylisoindolo[2,1-a]benzimidazole, is formed initially.…”

“…11H-Isoindolo[2,1-a]benzimidazole 3a is converted by the action of alkylating agents into the quaternary salts 55c-e, which are soluble in water [22]. When heated with acetic anhydride compound 3a is readily acetylated with the formation of the 5-acetyl derivative 56a, which is hydrolyzed by alkali to the initial base 3a.…”

“…This was used for the production of a series of cyanine dyes [22,74] -the styrils 57a and 57b [yield 73%, λ max 492 nm (log ε 4.67) and 22%, λ max 497 nm (log ε 4.83) respectively], symmetrical monomethinecyanines 58a and 58b [yield 19.8%, λ max 635 nm (log ε 5.15) and yield 18.5% respectively], and unsymmetrical dimethinecyanines 59a-l. …”

“…The formation of two products is possible during the reduction of compound 4a with lithium aluminum hydride [11,12,22,79,80]. Thus, only the alcohol 6 was obtained during the reaction in a mixture of ether and dioxane [11,12].…”

“…The yields of the hydrochloride amount to 40, 40, and 15% respectively[22].1a R 1 = R 2 = H; 15 a R 1 = H, R 2 = Et; b R 1 = R 2 = Et HCl 14 8-Aminotetrahydroquinoline can be used as diamine hydrochloride, and in this case the salt 16 is formed under similar conditions[23].…”