Reactions of 4-hydroxy-5,6,7,8-tetrafluorocoumarin derivatives with S-nucleophiles

In the reactions with o-aminothiophenol, 4-hydroxy-(3-(imino)acetyl)-5,6,7, 8-tetrafluorocoumarins give products of S-substitution at the C-7 atom. 7-S ubstituted 5,6,8-trifluorocoumarins form benzothiazole as a result of heter ocyclic ring opening; 3-ethoxycarbonyl-2-methyl-5,6,7,8-tetrafluorochromone undergoes acid splitting to 2-(2-hydroxy-3,4,5,6-tetrafluorophenyl)benzoth iazole. Under alkaline conditions, S-substituted coumarins decompose to ace tophenone. In an acid medium, 4-hydroxy-3-iminoacetyl-5,6,8-trifluoro-7-(2- aminophenylthio)coumarin affords 7-(2-aminophenylthio)-2-methyl-5,6,8-trifl uorochromone. 4-Hydroxy-5,6-difluoro-2-H-pyrano[6,5-a]phenothiazin-2-one wa s isolated from condensation of 7-(2-aminophenylthio)-4-hydroxy-5,6,8-trifl uorocoumarin in the presence of NaH. Reactions of 3-acetyl(iminoacetyl)-4-hydroxy-5,6,7,8-tetrafluorocoumarins a nd 3-ethoxycarbonyl-2-methyl-5,6,7,8-tetrafluorochromone with 2-mercaptoeth anol result in the formation of 5,7,8-trisubstituted derivatives. Interacti on of 3-ethoxycarbonyl-2-methyl-5,6,7,8-tetrafluorochromone with 2-mercapto ethanol, mercaptoacetic acid and 1,2-ethanedithiol leads to the formation o f the 7-substituted products. Acyl-lactone rearrangement of mono- and trisu bstituted chromones gives the corresponding coumarins. (C) 2000 Elsevier Sc ience S.A. All rights reserved.