Preparation of Quinoxalinecarboxylic Esters

Many such esters, both nuclear and extranuclear, have been made by primary synthesis (see Chapter 1) or by esterification of quinoxalinecarboxylic acids (see Section 7.1.2). The remaining methods are illustrated by the following classified examples. 

2-Quinoxalinecarbonyl chloride (56) (prepared in situ) and l-methyl-4-piper-idinol gave l-methylpiperidin-4-yl 2-quinoxalinecarboxylate (57) (pyridine, 

7-Dimethoxy-3-phenyl-2-quinoxalinecarboxamide (58) gave methyl 5,7-dimethoxy-3-phenyl-2-quinoxalinecarbixylate (59) (H2SO4, MeOH, 90°C, 

Note This process is surprisingly easy and deserves more frequent use. 

Ethyl 3-methyl-2-quinoxalinecarboxylate 1,4-dioxide (61, R = Et) gave methyl 3-methyl-2-quinoxalinecarboxylate 1,4-dioxide (61, R = Me) (Et3N, CaCl2, MeOH, 50°C, 2 h 80%).2  

Ethyl 3-methyl-2-quinoxalinecarboxylate (60, R = Et) gave 2-diethylaminoethyl 3-methyl-2-quinixalinecarboxylate (60, R = CH2CH2NEt2) (neat HOCH2 CH2NEt2, reflux, 4 h 21%) or 2-morpholinoethyl 3-methyl-2-quinoxaline-carboxylate [60, R = CH2CH2N(CH2CH2)20] [neat HOCH2CH2N(CH2 CH2)20, reflux, 4 h 66%].475 

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