Studies on pyrylium and thiopyrylium salts

Abstract

2H-Thiopyran-2-ones, 4H-thiopyran-4-ones, and 4H-pyran-4-ones may be reduced by lithium aluminum hydride to the corresponding thiopyranols or pyranols, which on treatment with perchloric acid are converted to pyrylium or thiopyrylium salts. The reaction fails with 2H-pyran-2-ones. Peracetate oxidation of 2H-thiopyran-2-thiones affords thiopyrylium salts, but with other pyran-2- and 4-thiones yields the corresponding ketones. The rearrangement of an acetylenic thiolester to thioflavone is described.