Cyclization Reactions of Nuclear Halogenoquinoxalines

Nuclear halogenoquinoxalines undergo a wide variety of cyclization reactions, both intra- and intermolecular. The following examples illustrate a selection of these. 

2-(A-Allyl-A-benzylamino)-3-bromoquinoxaline (202) gave l-benzyl-3-methyl-l//-pyrrolo[2,3-/7]quinoxaline (203) [Pd(OAc)2, K2CO3, Bu NBr, Me2NCHO, 80°C, 30 min 83%] analogs likewise. 

2-Chloro-3-(o-chlorophenylhydrazonomethyl)quinoxaline (204, R = H) gave 1-o-chlorophenyl-l//-pyrazolo[3,4- 7]quinoxaline (205, R = H) (diazabicy-cloundecene, Me2NCHO, reflux, 3h 83%) likewise 2-chloro-3-[a-(o-chlorophenylhydrazono-a-methoxycarbonylmethyl]quinoxaline (204, R = CO2-Me) gave methyl l-o-chlorophenyl-l//-pyrazolo[3,4- ]quinoxaline-3-carbox-ylate (205, R = C02Me) (diazabicycloundecene, Me2NCHO-dioxane, reflux, 2h 97%).  

3-Chloro-2-quinoxalinecarbonitrile (208) gave l//-pyrazolo[3,4-/ ]quinoxalin-3-amine (209) (excess neat H2NNH2 H20, reflux, 1 h 90% H2NNH2 H2O, 

3-Chloro-2-quinoxalinamine (210) and pyridine gave pyrido[l, 2 l,2]imi-dazo[4,5-fc]quinoxaline (211) (Mc2NCHO, 100°C, 48 h 49% note aerial oxidation). Several 3-substituted analogs were made similarly using appropriate pyridine derivatives.  

Intermolecular Cyclizations Involving Two Adjacent Halogeno Substituents 

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