Lithiation and Side-Chain Substitution of 3-Alkyl-1<i>H</i>-quinoxalin-2-ones

Abstract

3-Methyl-1H-quinoxalin-2-one has been doubly lithi­ated with n-butylithium at -78 °C in THF. The dilithio reagent thus obtained reacts with various electrophiles (iodomethane, iodoethane, D2O, benzaldehyde, benzophenone, cyclohexanone) to give modified 3-substituted 1H-quinoxalin-2-ones in good yields. In the reaction of the dilithio reagent with phenyl isothiocyanate the product was a tautomer of the simple substitution product. Reaction of the dilithio reagent with iodine gives an oxidatively dimerised product instead of the 3-iodomethyl derivative. Lithiations of 3-ethyl- and 3-propyl-1H-quinoxalin-2-ones, followed by reactions with representative electrophiles (benzaldehyde, benzophenone, cyclohexanone), behaved in a similar manner to give the corresponding modified 3-substituted derivatives in good yields.