Pyrido benzimidazoles

Structure-activity relationships of anxiolytic pyrido-benzimidazoles 184... 

STRUCTURE-ACTIVITY RELATIONSHIPS OF ANXIOLYTIC PYRIDO-BENZIMIDAZOLES... 

H-Pyrido[3,2-c]azepine, 7-methoxy-nucleophilic displacement reactions, 7, 514 Pyridoazepines synthesis, 7, 535, 540 Pyridoazepinones synthesis, 7, 531 Py rido[2,1-a]benzazepin-6-one physiological properties, 7, 546 Py rido[ 1,2-a]benzimidazoles reactions, 6, 1041... 

Electrophilic bromination (and nitration) of pyrido[l, 2-a]benzimidazole (analogous to 132) cannot take place in the imidazole moiety. Initial substitution, using NBS as reagent, was shown to occur at the 8-position, and subsequently at C-4 and C-6 (90JOU1166). 

A similar reaction of 1-arylacetylbenzimidazoles with dimethyl acetylenedicarboxy-late leads to pyrido[l,2-a]benzimidazoles ... 

Although the yields are only moderate, this method provides easy access to the pyrido[ 1,2-a]benzimidazole framework in a one-pot reaction.[155]... 

This indole synthesis has been extended to P-tetrahydrocarbolines (300) [371], azaketotetrahydrocarbazoles [372], carbolines, carbazoles, and pyrido[l,2-a]benzimidazoles [373]. Examples of the former two reaction types are illustrated. An early Heck cyclization of 2-carboxy-2 -iododiphenylamine to 1-carbazolecarboxylie acid (73% yield) [374] has been generally overlooked by subsequent investigators. 

When the reactions were carried out in chloroform for 2 hr, isopropyli-dene methoxymethylenemalonate reacted on the active methylene group of 2-benzimidazolylacetate and acetonitrile (1666) in the first step, and in the next step, one of the ring nitrogens was involved in a cyclization to give pyrido[l,2-a]benzimidazole-2-carboxylic acids (1667) in 86-89% yields (88YZ856). 

Das symmetrische 2,5-Bis-[2-pyridyl-amino]-l,4-dichlor-benzol setzt sich bei der Photolyse un-ter zweifacher Cyclisierung zu 13H-(Pyrido[l, 2-a]-(pyrrolo[2,3-h pyrido) [3,2-f]-benzimidazol ) (37%) um. Nebenprodukte sind.die monocyclisierten 8-(2-Pyridyl-amino)-[Pg.247]

The mesoionic pyrimidine 243349 (from carbon suboxide and 4,6-dimethyl-2-methylaminopyrimidine) added DMAD (and dicyanoacetyl-ene and 1,3-diphenyl- l-oxoprop-2-yne) in boiling xylene giving a good yield of the pyrido[l,2-a]pyrimidin-6-one (245). Phenylpropiolic ester and EP merely converted 243 back into 4,6-dimethyl-2-methylaminopy-rimidine. The fused pyrimidine 247, obtained from benzimidazole (246)... 

There has been a study of photo-induced intramolecular cyclization of some o-haloarylheterylamines which may lead to pyrido[l,2-a]benzimidazole derivatives.51 Several studies have been reported of photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reactions with fluoride,52 cyanide,53 or acetonitrile54 acting as the nucleophile. In the example illustrated in Scheme 3,... 

The benzo derivative (128) reacts as a thiocarbonyl ylide. Addition of N-(p-tolyl)maleimide gives a mixture of the exo (71%) and endo (16%) adducts (129 Ar=p-tolyl), which in hot acetic acid eliminate hydrogen sulfide giving the pyrido[l,2-a]benzimidazole (130 Ar=p-tolyl). Analogous 1 1 cycloadducts (131) are formed with dimethyl maleate, dimethyl fumarate, methyl crotonate and methyl acrylate. In contrast to the transformation (129) —> (130), treatment of the adducts (131 R = H, Me) with hot acetic acid gives the tetracyclic compounds (133) via the benzimidazole derivatives (132 R = H, Me). Reaction with alkynic 1,3-dipolarophiles gives pyrido[l,2-a]benzimidazole (134) by desulfurization of the primary adducts (80CL1369). 

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