Acid-Catalyzed Rearrangement of 3-Cyanoquinoxalin-2(1H)-ones When Exposed to 1,2-Diaminobenzenes: Synthesis of 2,2'-Bibenzimidazoles.

A novel and efficient protocol for the synthesis of diversely substituted 2,2'-bibenzimidazoles from the reaction of 3-cyanoquinoxalin-2(1H)-ones with 1,2-diaminobenzenes has been developed, which proceeds through sequential nucleophilic addition and electrophilic substitution followed by a Mamedov rearrangement. The synthetic utility of this strategy was illustrated by the concise, one-pot synthesis of 5,5'-bi(2,2'-bibenzimidazoles) and aza-analogues of 2,2'-bibenzimidazole.

One-Pot Synthesis of 7-(Benzimidazol-2-yl)thioxolumazine and -lumazine Derivatives via H2SO4-Catalyzed Rearrangement of Quinoxalinones When Exposed to 5,6-Diamino-2-mercapto- and 2,5,6-Triaminopyrimidin-4-ols.

A facile approach to a range of substituted 7-(benzimidazol-2-yl)thioxolumazines [7-(benzimidazol-2-yl)-2-thioxo-2,3-dihydropteridin-4(1 H)-ones] and 7-(benzimidazol-2-yl)lumazines [7-(benzimidazol-2-yl)pteridine-2,4(1 H,3 H)-diones] is described. These new biheterocyclic systems are obtained via H2SO4-catalyzed rearrangement of quinoxalin-2-ones in the presence of 5,6-diamino-2-mercapto- and 2,5,6-triaminopyrimidin-4-ols. Thus, benzimidazole and pteridine rings are constructed in one synthetic step. A plausible ANRORC ( addition of nucleophile, ring opening and ring closure)-type reaction mechanism is proposed. Applying the rearrangement to the aza-analogue of 3-benzoylquinoxalin-2(1 H)-one-i.e., 3-benzoylpyrido[2,3- b]pyrazin-2(1 H)-one-with 5,6-diamino-2-mercaptopyrimidin-4-ol makes it possible to synthesize inaccessible 7-(1 H-imidazo[4,5- b]pyridin-2-yl)-6-phenyl-2-thioxo-2,3-dihydropteridin-4(1 H)-one. 7-(Benzimidazol-2-yl)-6-(2-fluorophenyl)-2-thioxo-2,3-dihydropteridin-4(1 H)-ones undergoes intramolecular nucleophilic substitution of fluorine by a nitrogen of the benzimidazole fragment with the formation of benzo[4',5']imidazo[1',2':1,2]quinolino[4,3- g]pteridine-2,4(1 H,3 H)-diones as new heterocyclic systems.

Reaction for the synthesis of benzimidazol-2-ones, imidazo[5,4-b]-, and imidazo[4,5-c]pyridin-2-ones via the rearrangement of quinoxalin-2-ones and their aza analogues when exposed to enamines.

A synthetically useful protocol has been developed for the preparation of highly functionalized N-pyrrolylbenzimidazol-2-ones. The reaction of variously substituted 3-aroyl- and 3-alkanoylquinoxalin-2(1H)-ones with commercially available enamines in acetic acid results in a rapid rearrangement and formation of N-pyrrolylbenzimidazol-2-ones in modest to excellent yields. The key step of the rearrangement involves the novel ring contraction of 3-aroyl- and 3-alkanoylquinoxalin-2(1H)-ones with enamines. In this case, the atom of carbon which is displaced from the pyrazine ring of quinoxalin-2(1H)-one becomes the fourth carbon atom of the newly formed pyrrole ring. The method is applicable for the aza analogues of quinoxalin-2(1H)-ones.

The Dimroth Rearrangement in the Synthesis of Condensed Pyrimidines - Structural Analogs of Antiviral Compounds.

The review discusses the use of the Dimroth rearrangement in the synthesis of condensed pyrimidines which are key structural fragments of antiviral agents. The main attention is given to publications over the past 10 years. The bibliography includes 107 references.