Aryl(4metboxyphenyl and Znaphthyl)
and hetaryl(2furyl, 3-pyridyl, and 2-thienyl) 3-methyl-2quinoxalinyl ketones were pmpared via the reaction of bcnrofummn l-oxide (BFO) with 1-aryl-and 1-hetaryl-butane-13diones, followed by teduction of the resulting aryl or hetaryl3-methyl-2quinoxalinyl ketone 1 &dioxides with sodium dithionite. 1-(2-Furyl)butane-13-dione and l-(2-pyridyl)butane-13-dione yielded 2-acetyl-3-(2-f@)quinoxaline W-dioxide and 2-acetyl-3-(2-pyridyl)quinoxaline l&iioxide respectively as minor products on reaction with BFO. The effect of the structure of the hetaryl (or aryl) group in the 1,3diketone on the reaction with BFO is reported. As part of a study into the photochemistry of 2quinoxalinyl ketones, the 2-atoyl-3methylquinoxaJines 3a, 3b, 3c, 3e and 3f were prepared by sodium dithionite reduction of the corresponding quinoxaline 1 ,Cdioxides 7a, 7b, 7c, 7e and 7f. The latter compounds were synthesised by the well known Beirut reaction1 between benrofurazan l-oxide (BFO) (1) and the appropriate 1,3diketone 2 in diethylamine or triethylamine. The 1,3diketones were prepared according to the literature methods cited in the experimental section. The reaction of BFO (1) with unsymmetrical diketones 2 could, in theory, yield either or both of the two isomeric 2,3disubstituted quinoxaline l&dioxides 7 and 8. Formation of these products may result from cyclisation of intermediate 4* via nucleophilic addition of the hydroxylamine nitrogen at either of the two carbonyl groups, followed by dehydration. In the absence of other factors, cyclisation at the more electrophllic acetyl carbonyl group, leading to quinoxaline dioxide 7, should be favoured. Haddadin, Issidorides, and co-workers showed the intluence of steric and electronic effects on the regiospecificity of the reaction of BFO with a series of 1,3diketones 9.3 Smaller alkyl groups (R = Me and Et) and electrondonating aryl groups (Ar = Cmethoxyphenyl and p-tolyl) in the diketone 9 favoured the formation of 3-alkyl-*An intermediate of type 4 was proposed by Mason and Tennant.2