Preparation of Quinoxaline Ketones

The main preparative routes to quinoxaline ketones have been discussed earlier by primary synthesis (Chapter 1), by extranuclear acylation of alkylquinoxalines (Section 2.2.4), by oxidation of appropriate alkylquinoxalines (also Section 2.2.4), by displacement of a halogeno substituent (Section 3.2.7), by oxidation of 

Quinoxaline (199) underwent homolytic acetylation by acetyl radicals from biacetyl to give a chromatographically separable mixture of 2-acetyl- (200, R = H) and 2,3-diacetylquinoxaline (200, R = Ac) (reactants, H2SO4, AgNOs, H2O, 50°C then Na2S20g/H20i during 15 min and stirred 15 h 48% and 12%, respectively) (see Section 2.1.3). 

The unseparated mixture (201) of the cyclic acetals, 3-methyl-6- and 3-methyl-7-(2-methyl-l,3-dioxan-2-yl)-2-quinoxalmecarboxamide 1,4-dioxide (a product of primary synthesis see Section 1.6.7) gave a readily separable mixture of 6-acetyl- (202, Q = Ac, R = H) and 7-acetyl-3-methyl-2-quinoxalinecar-boxamide 1,4-dioxide (202, Q = H, R = Ac) (HCl, AcMe, H2O, reflux, 5 h  

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