Elimination, Ring-Contraction, and Fragmentation Reactions of 1-Thioflavanone 1-Oxides.

Epimeric thioflavanone sulfoxides (2b) were selectively transformed into thioflavone (1a), thioaurone (3a), and di(2-cinnamoylphenyl) disulfide (4). Disulfide 4 can be recyclized into thioaurones (3a–c) and thioflavanones (2a,5) with heterolysis of the S—S bond. The 3-p-anisylidene sulfoxide analog of 2b (6) transforms, with fragmentation, into 4'-methoxythioaurone 3b.Key words: chalcone, ring contraction, sulfoxides, thioaurones, thioflavonoids.