Abstract
ABSTRACT
3-Methyl-1H-quinoxaline-2-thione (1) has been doubly lithiated, at nitrogen and at the 3-methyl group, with N-butyllithium at -78 °C in THF. The resulting dilithium reagent obtained reacts with a variety of electrophiles (iodomethane, iodoethane, 1-bromobutane, D
2
O, benzaldehyde, anisaldehyde, 2-hexanone, cyclohexanone, benzophenone, phenyl isothiocyanate) to give the corresponding modified 3-substituted 1H-quinoxaline-2-thiones 4-13 in high yields. Similarly, double lithiation of 3-ethyl- (4) and 3-propyl-1H-quinoxaline-2-thiones (5), followed by reaction with some electrophiles gave the corresponding modified 3-substituted derivatives 15-19 in high yields. Treatment of some of the products with trifluoroacetic acid in dichloromethane at room temperature led to formation of substituted 2,3-dihydrothieno[2,3-B]quinoxalines in good yields.