Contribution to the Transformations of 1‐Thioflavonoids with Hypervalent Oxidants.

Permanganate oxidation transforms 1-thioflavanone (1a) to the corresponding 1,1-dioxide 1c. Periodate oxidation of 1a affords in the cold mainly the corresponding sulfoxide 1b, and that of 1a or 1-thioflavone 1-oxide (2b) provides on heating 1-thioflavone 1,1-dioxide (2c). Since 1b is resistant to ceric ammonium nitrate (CAN) the mechanism of the dehydrogenation reaction of 1a with CAN furnishing 1-thioflavone (2a) with transient formation of 1b, as suggested in the literature, is questionable.