A simple regioselective synthesis of pyrimido[1,2‐a]benzimidazoles

Abstract

2‐Aminobenzimidazoles were reacted with enaminones in acetic acid to give pyrimido[1,2‐a]benzimidazoles. With a substituted enaminone only one regioisomer was obtained. Structural assignments based on nmr and uv spectroscopy are presented. Possible pathways leading to the products are discussed.

Studies with 2-arylhydrazono-3-oxopropanals: Routes for the synthesis of pyridazine-3,4-dicarboxylate and 3,5-diaroyl pyrazoles

“…1,7 However, only moderate yields of the desired products 2a-e were obtained. Consequently we have modified this synthetic approach and condensed these ketones with DMFDMA in absence of solvent.…”

Synthesis of a new tricylic ring system: [1,2,3]triazolo[1,5-b]cinnolinium salt

“…While reproduction of the first reaction step (i.e. 3 → 4) took place in excellent yield, 5 we had to encounter some difficulties with the subsequent two reaction steps: rather low yields and intensive decompositions were experienced. As a result of an ongoing search for suitable reaction conditions for the desired synthesis, however, we have found that by the help of two modifications both transformations can be carried out in satisfactory and well reproducible yields.…”

Synthesis, cyclooxygenase inhibition, anti-inflammatory evaluation and ulcerogenic liability of new 1,5-diarylpyrazole derivatives

“…The enaminone derivatives (8a-d) were prepared via condensation of the appropriate aryl or heteroaryl methyl ketone with dimethylformamide dimethylacetal (DMFDMA) in xylene following procedures applied in literatures [15][16][17][18][19][20][21] . Cyclocondensation of the appropriate enaminone (8a-d) with 4-hydrazinylbenzenesulfonamide hydrochloride (9a) 22 , methanesulfonylphenylhydrazine hydrochloride (9b) 23,24 or 4-hydrazinobenzoic acid (9c) 25 in aqueous ethanol afforded the respective 1,5-diarylpyrazoles (10a-l) in good yields (56-88%) (Scheme 1).…”

“…Silica gel column chromatography was performed using Merck silica gel 60 ASTM (70-230 mesh). Compounds 8a-d [15][16][17][18][19][20][21] , 9a-c [22][23][24][25] were prepared according to the reported procedures.…”