New domino reaction. One pot synthesis of 4,7-dihydroxythioaurone derivatives from benzaldehydes and 4-acetyl-2-oxo-benz[1,3]oxathiole

A convenient synthesis of 4,7-dihydroxythioaurone derivatives by a one pot reaction of benzaldehydes with 4-acetyl-2-oxo-benz[1,3]oxathioles and piperidine acetate in DMSO is described. The structures of the compounds, including double bond geometry were proved unequivocally by NMR methods. The thioaurone ring system seems to be formed by three consecutive reactions: opening of the oxathiolone ring with piperidine, oxidation of the formed mercapto group with DMSO or/and air to disulfide, and condensation with aldehyde.