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Presented herein is a novel synthesis of new 2-(quinolin-4-yl)-1,4-dihydroquinazoline systems 8 , in which the acid-catalyzed rearrangement of spiro[benzo[ e ][1,4]diazepine-3,4'-quinolin]-2(1 H )-ones generated in situ from 3-(2-aminophenyl)-5 H -benzo[ e ][1,4]diazepin-2(1 H )-ones 6 with acetone and alkylmethyl ketones has been realized as an important step. An attempt to synthesize isomeric 2-(2-aminophenyl)-5 H -benzo[ e ][1,4]diazepin-3(4 H )-one 6'a by hydrolysis of the corresponding N -{2-[5 H -benzo[ e ][1,4]diazepin-3(4 H )-on-2-yl]phenyl}acetamide 5'a led to a new heterocyclic system, 6-methyl-8,13-dihydro-13a H -quinazolino[4,3- b ]quinazolin-5-ium 13a-carboxylate 14 , as a result of an unexpected rearrangement. In addition, it is noteworthy that during the hydrolysis of N -{2-[5 H -benzo[ e ][1,4]diazepin-2(1 H )-on-3-yl]phenyl}acetamides 5 , the not previously described 14-dihydro-5 H -14,5a-(epimino[1,2]benzo)benzo[5,6][1,4]diazepin[2,1 -b ]quinazolin-6(7 H )-ones 7 were unexpectedly obtained.

A facile and direct intramolecular indolinone-quinolone rearrangement was developed for the synthesis of quinolino[3,4- b ]quinoxalin-6-ones from spiro[indoline-3,2'-quinoxaline]-2,3'-diones, which are readily available with use of isatines, malononitrile, and 1,2-phenylenediamines under quite mild conditions. This efficient approach provides excellent yields and could potentially be used for the construction of a diverse library of quinolino[3,4- b ]quinoxalin-6-ones for high-throughput screening in medicinal chemistry. The reaction mechanism is explored by extensive DFT calculations.

Herein, we report a highly regioselective one-pot synthesis of pyrazolo[3,4- b ]pyridines via the reaction of 3-arylidene-1-pyrrolines with aminopyrazoles. The reaction proceeds through the sequential nucleophilic addition/electrophilic substitution/C-N bond cleavage and provides easy access to pyrazolo[3,4- b ]pyridine derivatives featuring a primary amino group. Moreover, the reaction can be terminated at the electrophilic substitution stage, thus providing convenient entry to the hardly accessible pyrazolopyrrolopyridine scaffold.

A new process has been developed for the bromine-promoted sequential (sp 2 )C = (sp 2 )C bond functionalization of ( E )-3-styrylquinoxalin-2(1 H )-ones and furo[ b ]annulation via the 5- exo- cyclization in dimethyl sulfoxide (DMSO). The reaction represents a novel strategy for the synthesis of 2-aryl-3-(methylthio)furo[2,3- b ]quinoxalines and involves 3-(1,2-dibromo-2-arylethyl)quinoxalin-2(1 H )-ones and 2-arylfuro[2,3- b ]quinoxalines as key intermediates. Furthermore, DMSO was converted to dimethyl sulfide in situ, which served as the methylthiolation reagent in the reaction. This protocol constitutes an efficient and convenient method for the annulation and methylthiolation of ( E )-3-styrylquinoxalin-2(1 H )-ones bearing a wide range of functional groups in high yields at room temperature.

A novel and efficient protocol for the synthesis of diversely substituted 2,2'-bibenzimidazoles from the reaction of 3-cyanoquinoxalin-2(1 H )-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.

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 H 2 SO 4 -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.