1H- and 1-alkyl-1,4-dihydro-4-oxo-3-alkylthioquinolines from 1,4-dihydro-4-oxo-3′-alkylthio-3,4′-diquinolinyl sulfides

Quinolinones (1) were N-alkylated with alkyl iodides in DMSO or DMF in the presence of potassium methoxide to N-alkyl derivatives (3) (78-98%). One-pot method was elaborated allowing to transform compound (1a) into the mixture of 1-alkyl-3-alkylthio-4(1H)-quinolinones (8) (55-76%) and 4-methoxy-3-methylthioquinoline (4a) (83-90%). Potassium methoxide in DMSO causes sequentially fission of diquinolinyl sulfide (1) to the mixture of dipotassium salt of 3-mercapto-4-quinolinone (9) and (4) and then O-demethylation of 4 to potassium salt of 3-alkylthio-4-quinolinone (5), which could be transformed after S-alkylation of 9 and neutralization to 3-alkylthio-4-quinolinones (6). This one-pot procedure permits to convert both quinoline-units of 3,4'-diquinolinyl sulfide (1) to 6 with total yield of 60-78%.