Benzimidazole 2-methyl-5,6-dibromo

Quinoxaline-2,3-dione is converted into 2,3-dichloroquinoxaline by phosphoryl chloride142 or phosphorus pentachloride.143 2,3-Dibromo-quinoxaline is similarly obtained using phosphoryl bromide in dimethyl-aniline.144 Quinoxalin-2-one undergoes ring contraction to 2-methyl-benzimidazole (134) with hydrazine145 however, quinoxaline-2,3-dione gives 3-hydrazino-2-quinoxalinone.145 Quinoxalin-2-one yields a 3-p-dimethylaminophenyl derivative with 7V,N-dimethylaniline (in AcOH, with NH4N03), and a 3-(indol-3-yl) derivative with indole.146... 

Under the influence of nitrosylsulfuric acid, 2-amino-5- and -6-bromo-l-methylben-zimidazoles (183) are converted, as a result of self-coupling, into the 2, 5- (184) and 2, 6-(185) azobenzimidazoles. Even the 5,6-dibromo analogues can react in a similar way by loss of one of the bromine atoms (Scheme 94) (72CHE1533). Coupling with diazonium salts of 4-amino- and 2-methyl-4-amino-benzimidazole occurs at C-7, while a protected 4-amino group (acetylated) directs nitration into both the 5- and 7-positions. A 4-fluoro substituent likewise leads to 7-nitration (74CRV279). 

Reactions.— The nucleophilic reactivity of the thiocarbonyl sulphur atom in thioureas has been further exemplified in a series of papers reporting on S-alkylation reactions of open-chain " as well as cyclic thioureas using alkyl halides. Ried and his co-workers have reported that (4-quinazolyl)thioureas (315) react smoothly with methylene iodide in the presence of triethylamine to yield the 1,3-thiazetidines (316). The ready formation of (316) was attributed to the special effect of the intramolecular hydrogen bonding in (315), as common thioureas usually did not enter into this reaction in a well-defined and profitable way. 5,5-Diphenyl-2-thio-hydantoin reacted with symmetrical ao>-dibromo-alkanes to yield the cyclization products (317). The action of excess of methyl iodide on N -substituted N-(o-aminophenyl)thioureas afforded the benzimidazoles (318), alternatively obtainable by treatment of the same thioureas with mercuric chloride." " In a similar manner, l-amino-6,7-dimethoxy-3,4-di-hydroisoquinolines were formed by the action of mercuric chloride on the thioureas (319)" or their S-methyl derivatives (320). " A recent paper by Klayman and his co-workers deals with the reactivity of S-methiodide derivatives of thioureas that are activated by electron-withdrawing groups towards hydroxylic compounds. "... 

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