Ethyl 3-amino-2- quinoxaline

The alternative Scheme B is based on A-nucleophilic attack. Thus, bubbling air through a boiling solution of ethyl 3-amino-2-(quinoxaline-2-carbonyl)crotonoate 66 in DMF furnishes pyrido[2,3-Zr]quinoxaline 67 (Scheme 20) (04RCB1267). The latter has a structural similarity to derivatives of 4-quinolone-3-carboxylic acid, well known because of their high antibacterial activity. 

Chloro-3-methylquinoxaline 4-oxide gave 3-chloro-2-quinoxalinecarbalde-hyde 1-oxide (172) (SeOi, PhH, reflux, h 72%) dioxane may be used as solvent for such oxidations yielding, for example, 3-amino-2-quinoxaline-carbaldehyde ethyl acetate may also be so used. 

Bis(bromomethyl)quinoxaline (296) gave either 6,8-dihydrofuro[3,4-g]qui-noxaline (297) (NaOH, H20-MeCN, BU4NHSO4, no further details 84%) or ethyl 7-isocyano-7,8-dihydro-6//-cyclopenta[g]quinoxaline-7-carboxylate (298) (Et02CCH2NC, K2CO3, BU4NHSO4, MeCN, no further details 38%) and thence the 7-amino ester (HCl-EtOH, no further details 90%). ... 

Note These examples are extensions of the Friedlander quinoline synthesis. 3-Amino-2-quinoxalinecarbaldehyde (183, R = H) and diethyl malonate (184) gave ethyl 2-oxo-l, 2-dihydropyrido[2,3-/ quinoxaline-3-carboxylate (185, R = H) (trace NaOH, trace H20, EtOH, 10 min 60%).143... 

Cyclization of 6-benzoyl-3-amino-2-imino-2,3-dihydrothiazolo[4,5-A quinoxaline 260 was achieved upon treatment with ethyl cyanoacetate in DMF/Et3N to yield [l,2,4]triazolo[3, 2 3,2]thiazolo[4,5- ]quinoxaline derivative 261 (Equation 34) <2000PS(157)87>. 

A few extensions of the Conrad-Limpach synthesis have been applied to the synthesis of 4,7-phenanthrolines. Unlike o-phenylenediamine, which gives a quinoxaline derivative, p-phenylenediamine reacts with excess of ethyl ethoxalylpropionate to give an intermediate bisanil, which cyclizes in hot diphenyl ether to afford 3,8-dicarboethoxy-l,10-dihydroxy-2,9-dimethyl-4,7-phenanthroline in high yield.237 With diethyl ethoxymethylenemalonate as condensing agent, 6-amino-8-methoxy-quinoline has been converted into 2-carboethoxy-l-hydroxy-6-methoxy-4,7-phenanthroline.238 A related condensation affording 1-... 

Reactions of 2-chloro- and 2,3-dichloroquinoxalines with carbanions give 2-quinoxalinyl ketones and 3-chloro-2-quinoxalinyl ketones, respectively e.g., 2-quinoxalinylacetophenone (151) from acetophenone anion.161 However, 2,3-dimethoxy- and 2,3-diethoxy-quinoxaline with methyl ethyl ketone and sodamide in anhydrous benzene give 2-amino derivatives rather than ketones.162... 

---