An Advantageous Synthesis of 2-Substituted Benzimidazoles Using Polyphosphoric Acid. 2-(Pyridyl)-1H-benzimidazoles, 1-Alkyl-(1H-benzimidazol-2-yl)pyridinium Salts, their Homologues and Vinylogues

Betaines of pyridinium benzimidazolate containing polymethylene interannular spacers

“…1-Decyl-4-[2-(2-benzimimidazolyl)ethyl]pyridinium salt 8a was prepared in two steps from pyridylvinyl derivative 12, 6 and was then reduced with Pd-C 10% to pyridylethyl derivative 13.…”

“…Quaternization of pyridine was carried out with bromoalkyl acid 17-18 to obtain pyridinium derivatives 19-20, which were then efficiently transformed into targeted salts 9a,b and 10a,b by reaction with phenylenediamine 16a,b by Hein's modified benzimidazole synthesis. 6 Transformation of the aforementioned pyridinium salts 8b, 9b and 10b into the corresponding inner salts 5b, 6b and 7b was carried out exploiting our standard protocol, [1][2][3][4] …”

“…In order to study this transformation, 1 H NMR spectra in DMSO-d 6 of 8a was registered, and then a drop of tetrabutylamonium hydroxide was added to the solution. Chemical shifts of the new spectrum indicated that 1,4-dihydropyridine 21 was formed in basic solution (See Figure 2), and decomposition compounds were formed in 24 hours at room temperature.…”

“…If TFAA was added to the initial basic solution, pyridinum salt 8a was recovered. An 1 H NMR spectrum in DMSO-d 6 of solid compound obtained from fast treatment (less than 1 minute) with Amberlite IRA-401 resin (OH -form) showed that dihydropyridine 21 was the main component.…”

Silica Supported Fluoroboric Acid: An Efficient and Reusable Heterogeneous Catalyst for Facile Synthesis of 2-Aliphatic Benzothiazoles, Benzoxazoles, Benzimidazoles and Imidazo[4,5-b]pyridines

“…1,2 These heterocycles have achieved significance in pharmacology as antibacterial, 3 antiviral, 4 antifungal, 5 anticancer, 6 anticonvulsant 7 and immunosuppressant agents. 8 Quite a plethora of methods have been developed for the preparation of these heterocycles including the condensation of carboxylic acids, 9 acid chlorides, 10,11 orthoesters, [12][13][14] esters, 15 and aldehydes [16][17][18][19][20][21] with o-aminophenols, o-aminothiophenols and o-phenylenediamines, dehydration of o-acylaminophenols, 22 the reaction of o-quinones with amines 23 and Beckmann rearrangement of o-acylphenoloximes. 24 However all of these procedures suffer from one or more of the following drawbacks such as long reaction time, low yield of the products, harsh reaction conditions, use of excess amount of reagents, tedious work up procedures and co-occurrence of several side reactions.…”