Reaction of 4-hydroxy-2-quinolones with thionyl chloride—preparation of new spiro-benzo[1,3]oxathioles and their transformations

4-Hydroxy-2-quinolones (1) react with thionyl chloride to give new spiro-benzo[1,3]oxathioles (3) and bis(4-hydroxy-2-quinolone-3-yl)sulfides (2) and small quantities of 3-chloro-4-hydroxyquinolin-2-ones (4). Compounds 3 afford sulfides 2 by heating in different solvents and [1,4]oxathiino[3,2-c:5,6-c′]diquinoline-6,8(5H,9H)-diones (6) by reaction with triphenylphosphine. The reconversion of compounds 2 to 3 was achieved using bromine. The reaction mechanisms are discussed for all transformations. All compounds were characterized by IR, 1H, and 13C NMR (in some cases also 15N NMR) spectroscopy, and EI and/or ESI mass spectrometry. The X-ray structure was determined for compound 3b.