Preparation of Quinoxalinecarboxylic Acids

Two routes to quinoxalinecarboxylic acids have been covered already by primary synthesis (see Chapter 1) and by oxidation of alkylquinoxalines (see Section 2.2.4). The remaining methods are illustrated by the following classified examples. 

Quinoxalines Supplement II, Chemistry of Heterocyclic Compounds, Volume 61, by Desmond J. Brown ISBN 0-471-26495-4 Copyright 2004 John Wiley Sons, Inc. 

Such hydrolyses may be done in aqueous alkali, in aqueous organic base, or under acidic conditions. 

Methyl 6,7-dimethoxy-4-methyl-3-oxo-3,4-dihydro-2-quinoxalinecarboxylate (1, R = Me) gave 6,7-dimethoxy-4-methyl-3-oxo-3,4-dihydro-2-quinoxaline-carboxylic acid (1, R = H) (IM NaOH, 20°C, 79 min 79%).  

Methyl 2,3-dimethoxy-6-methyl-7-nitro-5-quinoxalinecarboxylate (2, R = Me) gave 2,3-dimethoxy-6-methyl-7-nitro-5-quinoxalinecarboxylic acid (2, R = H) (KOH, H2O, THF, 20°C, 27 h 95%).  

---