Reaction of 3-methyl-2(1H)quinoxalinone (1) with alkyl, benzyl, and arenesulfonyl halides in the presence of K2CO3 in dry acetone gave 1-substituted 3-methyl-2(1H)-quinoxalinones (2a–g). However 1 reacts with benzoyl chloride under the same conditions to give 3-methyl-2-quinoxalinyl benzoate, while it reacts with P2S5 in dry pyridine to give 3-methyl-2(1H)quinoxalinethione (4). Treatment of 4 with methy iodide in the presence of K2CO3 in dry acetone gave 2-methyl-3-(methylthio)quinoxaline but not 1,3-dimethyl-2(1H)-quinoxalinethione which has been obtained from 2a and P2S5 in dry pyridine. Treatment of 4 with benzyl bromide and/or p-nitrobenzyl bromide in the presence of K2CO3 in dry acetone gave 2-benzylthio and 2-(p-nitrobenzylthio)-3-methylquinoxalines. Syntheses of 1-methyl-3-(substituted styryl)-2(1H)-quinoxalinone (8a–m) were achieved by condensation of 2a with aromatic aldehydes. Addition of thiophenols and mercaptoacetic acid to 8 gives 1-methyl-3-[2-(substituted phenylthio)ethyl]-2(1H)-quinoxalinones and 1-methyl-3-[2-(substituted phenyl)-2-(carboxymethylthio)ethyl]-2(1H)-quinoxalinones respectively. 1,3-Dimethyl-2(1H)-quinoxalinone (2a) condensed with ketones in the presence of ZnCl2 to give 1-methyl-3-[2-(substituted phenyl)-1-alkenyl]-2(1H)-quinoxalinones. 1-Methyl-3-(substituted styryl)-2(1H)-quinoxalinethiones were produced by refluxing a mixture of 8 with P2S5 in dry pyridine